There is no right or wrong way to do this. There is no such thing as the "perfect" board, otherwise they would all look the same. Every SUP is a compromise in some way.
The first decision you have to make is between a displacement or planing hull. A displacement hull (what most people will call a racing SUP) has the enormous advantage of speed. Because of their narrow, toothpick shape, however, they also tend to be very tippy. This is compounded when 100 pounds of gear and fish are added to the board. Because these boards are typically made with lighter and more expensive materials, they also can cost a lot of money. A planing style hull is your standard "surf board" style. These tend to be much slower, wider, and more stable than a race shape. They are also abundant and can often be picked up for incredibly cheap. Ultimately, I always prefer a displacement hull. My number one priority is speed, getting out to the reefs and back as quickly as possible.
Your next decision will be size. The bottom line is this: the more volume a board has, the better it will be for hunting and hauling gear. Most people are at least somewhat limited, however, whether it be by storage, transportation, or just the ability to carry the board. In a race shape, the absolute minimum size I would recommend is 12'6". This is sort of the standard "small" race board size, and they are readily available. Even at 12'6", however, I would recommend looking for a higher-volume specimen. This means looking for a wider, thicker board. I have hunted from race shapes as small as 12'6"x24", and I could only paddle with all my gear in ideal conditions. Also consider that when a lower volume board is weighed down, the speed will be affected much more than a higher volume board carrying the same weight. My recommendation is to stick with a 14' stock race board, if you have the means to store it. The next step up would be what we call an "unlimited" race board, which are typically 17-18'. My current board is 17'. The unlimited boards are ideal, but these are expensive and much more difficult to find, not to mention hard to carry, store, and transport.
I have found that there is 1 universal law of diving from a SUP: Anything that is not physically tied to the board will fall off and be lost to the depths. No exceptions. The first thing you're going to need to combat that is a tie down system. There are a few different ways to do this, and we'll explore the ones that have worked best for me.
All of my preferred methods center around using a bungee. To me, this is the most fool proof way to mindlessly keep gear tight to your board. My favorite method is to use GoPro mounts, as pictured below. I use the surf mounts because they have a larger surface area and can handle a higher load. Start by drilling a hole just big enough for a small length of mono to fit through (I use 300# for everything). Take a lighter and heat each end until it mushrooms out just a bit. Let cool, and it'll be stuck there forever.
Make sure that you clean the area you are sticking the mounts to extremely well. I scuff the area with sand paper and then wipe down with alcohol. Stick your mounts on, but let them sit for at least 24 hours before applying the bungee or any other load. After waiting a day, thread your bungee, and you have an extremely durable cargo net. I have some examples going on 2 years that have required no maintenance.
If you are trying to attached gear to a flat section of your board, or simply want to be a little more low-profile, a similar option is to use these small circle mounts with a loop of mono to thread the bungee. I found these to work well but are not as suitable for heavy stress.
Either of these ideas will serve you well. Remember, all of your expensive dive gear depends on your tie downs. If it's not tied down, it WILL go overboard.
Everyone wants to go fast, but one of the most important jobs of your SUP is to not move at all while you're diving. As all SUPs have a leash plug that is suitable for high stress loads, this is a pretty easy step to get right. Getting it as clean and as functional as possible is another story altogether. Below we will explore a few decent options.
My current anchor method of choice is using a speargun reel mounted to the front of the SUP. I happen to have an FCS fin plug mounted in my boat stock, but this could be easily added and the plugs are available on Amazon. Basically, I use various GoPro accessories to build a mount to fit my reel. Below is a Red Tide reel that holds 30 meters of spectra. This reel has the advantage of being easily removable from the base, but that can also be a disadvantage if it pops off when you don't want it to. The whole assembly is easily removed with an FCS fin key. The line has a breaking strength of around 1000 pounds, so nothing to worry about there.
The reel I've been using recently is an Ulusub with 50 meters of line capacity. Using the same FCS plug, I am able to make this reel sit flush with the board, and it is extremely sturdy. The process of removing it requires one extra step, but it also will never pop off on accident. I attach the line to a 3 pound stainless steel grappling anchor. I tried a 1.5 pound anchor, and it works fine in calm conditions or when hooked to structure, but will slip on a sand bottom when there is wind or current. The anchor can be tucked away in a fin foot pocket for travel. Overall, this is my favorite setup to date, and I highly recommend it.
Another method I have used are basic little boat cleats. These also make it easy to store line and tie off accurately without tangles. The problem with the method below was that it is very difficult to operate an anchor system all the way at the back of the boat. ...basically you have to be in the water to work it. This will work, but it's not my favorite.
Finally, if you just need a line in a pinch and you know about what depth of water you'll be in, you can simply wrap a length of line around an anchor for travel and tie it off to the leash plug. This is difficult and messy to operate, but it will get the job done just fine.
Ah. The dive flag. A pesky and vital piece of gear. I have found this to be the most technically challenging piece of gear to get right on a SUP. I have found at least 4 good options, so lets explore them.
The absolute, hands down, best way to mount the dive flag is to... ::cringe:: ...drill a hole in your board and epoxy in a tube. You can then just drop in a flag pole (I like using a pole spear) that will never fall out or fall over or break. This method can be seen below.
...but what if you don't want to take a power drill to your new $5k carbon fiber board? Completely understandable. But, that's where this gets a little more tricky. Without permanently modifying the board, there's not a really sturdy option for mounting a flag. This leaves us 2 choices: an unsteady flag, or mount it to something else.
Enter: Yeti. If you choose to use a cooler (this will be addressed next), the cooler will be your best option for mounting a flag. Conveniently enough, Yeti coolers accept a fishing rod holder in a very sturdy fashion that will hold a dive flag made to fit flush in a fishing rod holder. This option is awesome. It is as sturdy as modifying the board, but easily removable. The downside? ...to be discussed in the next section, but a Yeti is HEAVY and has limited space. Weight is EVERYTHING when building a SUP for long distance travel, so this option may not be right for you.
Okay, so you're going to use a lightweight cooler instead. Great. But, you won't find one that will accept a fishing rod mount as well as the Yeti. I have experimented with making my own flag pole holder out of a PVC tube attached to the cooler, and it tends to work pretty darn well. If you are searching for a lightweight cooler option, this one isn't bad.
Then again, maybe you're just diving and don't need a cooler. Or, maybe you don't want to drill holes in your otherwise nice cooler. Fine. There's still an option for you. I keep 2 or 3 GoPro surf mounts (sensing a theme here?) mounted in my "cockpit" near the front of the board. These typically hold my electronics, cameras, etc, but when in the water, they can also hold a dive flag. The catch here is that it is really not easy to make a flag that will sit securely in a GoPro mount. I've found your best shot is to use a flag that is as short and lightweight as possible. It will work, but it's not tough. I've broken several flag set ups this way just by bumping them on accident. This is a great, lightweight option (I am a weight weenie), but it has its drawbacks.
Don't like any of these ideas? ...I've tried at least 10 other methods, these are just the ones that have worked best for me. Try your own, there are a million ways to make this work.
This will come to be the bane of your SUP hunting existence. It is an inconvenient truth that you have to get your fish home, and if you have any respect you'll get them home cold. The problem is that fish and ice are, by far, the heaviest part of the haul. Again, weight is everything. Let's explore some options that have worked well for me.
Option 1 is the Yeti. As previously discussed, this will give you the ability to mount a really sturdy dive flag, so it's got an advantage from the start. The other huge advantage? ...dude, it's a Yeti. You can paddle all day in 100 degree heat down here in Florida and all your ice will still be there at the end of the day. However, there are significant drawbacks. It my mind, the most significant is the weight. The Yeti itself weighs 17 pounds. While I would never accept 17 pounds of dead weight, when taken in context of 20 pounds of ice and 50+ pounds of fish, the weight could be overlooked for its utility. The real problem is the distribution of the weight. There is a lot of weight in the lid of the Yeti, and the whole cooler rises up above the deck of the board. Especially when the cooler is loaded with ice and fish, it make the SUP very tippy and more reactive to swell. In choppy conditions, this can quickly become a nightmare, and indeed, I have had to knee paddle 7 miles home in the open ocean because of this.
But wait, there's more. The capacity of the Yeti is relatively limited. The Yeti 45 is the biggest model I can fit on my board, and it will hold a limit of hogs, but it certainly will not fit a 50 pound cobia or AJ. You land one of those and you're out of luck.
The cheaper, and I argue probably better, cooler option is a $30 50qt Igloo from Walmart. These weigh maybe 2-3 pounds, and their capacity is significantly more than a Yeti (I actually have curled up a 50# cobia with the tail handing out in one of these). Obviously, this helps to mitigate 2 of the bigger issues with the Yeti, but of course this comes at a cost. Obviously, this won't hold ice like a Yeti, but if you take 20 pounds, it'll probably last a full day on the water. Secondly, as noted in the previous section, the flag mounting options are not as good as with the Yeti. Even with a lighter cooler, there is a significant issue with the coolers rocking in swell. This is a significant drawback that should not be overlooked.
My current set up is a 65"x20" Wahoo insulated fish bag. I fold the bag in half, so it only take up about 30" of space. It weighs only a couple of pounds, and it holds ice all day. The bag has 2 huge advantages. It it very light, but more importantly, all of the weight is concentrated very low and it cannot cause instability the way the coolers do. Secondly, I can fit any fish I catch in the bag. I typically leave it folded in half to conserve space, but it only has to be unfolded to accommodate a very long fish. The drawback is that the bag is not durable like a cooler. I'm paranoid about spines puncturing the bag, so I put really spiny fish inside a tough dry bag before putting them into the fish bag. The fish bag also cannot hold a dive flag, so you'll have to choose one of the non-cooler options for dive flag mounting. Overall, the bag is the best I've found so far for weight, stability, and capacity.
If you really want to take your SUP hunting game to the next level, you're really going to need electronics. This is a little tricky, as there is no power on a SUP! There are 2 directions you can go:
1: You can carry a 12 volt battery around and somehow try to make it water proof
2: Carry electronics that are self-powered.
I prefer option 2 by a long shot. I start with a handheld Garmin Marine GPS. I keep it in a dry bag that is mounted in my "cockpit". This carries all the numbers for all my local reefs and navigates me to them in real time. It is important you have a screen that is clearly visible while paddling so that you don't have to continually stop to make adjustments to your bearing.
The second crucial piece of gear is a bottom finder of some sort. I use a little sonar ball made by Fish Hunter that syncs with my phone. I only use this to find the reefs once I know I am close by GPS. This little units actually maps the ocean floor in 3D and is really a game changer for the SUP. It weighs probably about a pound and takes up virtually no space, yet provides priceless data. Another option would be a basic little AAA powered depth finder, which can be had off Amazon for around $100.
Really, this should be step 1. Diving and spearfishing are dangerous adventures in their own right. When you're diving from a tiny paddle boat out in the middle of the ocean, things can go horribly wrong. You can mitigate some of these risks, however, with gear you might find on any regular boat. I have a small Pelican Case that I throw all my safety gear in. Here are a list of safety items that I never paddle without:
The first thing that everyone should have at all times with no excuses is a cell phone. On a SUP, you're USUALLY going to be in range of some kind of service in case of emergency. You can call 911 and they will forward you to the Coast Guard. Keep it in a dry bag so that there's no chance of it getting ruined.
The next mandatory piece of gear is a VHF radio with DSC. There are a lot of options for this, but I use a Nautilus Lifeline because it is waterproof and made for diving. As a dedicated VHF, it would be pretty weak, but it is made to be a safety tool and will get you out of a jam. There is a dedicated panic button that will alert all vessels in the area of your location and distress. This tool is your fastest lifeline to help if something goes wrong out in the ocean.
I also like to keep a small EPIRB with me. I'm not usually far enough out in the ocean that I would need to escalate past options #1 and #2, but this little guy is peace of mind. Push the button and the Coast Guard is coming to get you anywhere, anytime. The drawback is that this could take hours, while the VHF/DSC can get you help from nearby boats in minutes.
Beyond these safety gadgets, you also need to be prepared to handle life threatening emergencies on your own until help arrives. I carry a small number of vital tools for stabilization. It is helpful to have two tourniquets for hemostasis in case marine life with teeth or your buddy with an errant spear hits a major artery. I also carry a SAM splint and duct tape. These basic tools are invaluable if things go wrong in the middle of the ocean. My own preference is to carry some epinephrine as well, since there are all kinds of stinging animals out there, and I don't know how I react to all of them yet.
Lastly, make sure you have a PFD. It takes basically no room, and I know people who have had their lives saved by having this on board. ...not to mention, you are eligible for a ticket if caught on a SUP without one.