Some of my most successful outings have been from a kayak. I have dove and fished off my "fleet" of yaks for years now and really, really enjoy it. I also have a 23' Parker Pilothouse boat and frankly whenever I'm on a yak, I miss being able to move 5 miles to a new spot and whenever I'm on the Parker, I miss being able to get in tight to the kelp and rocks (and the exercise).
Definitely take a "backpacker" approach to weight consciousness; if you are overloaded, it will really cut down on the fun.
I started out on a 80 lb Hobie (now nicknamed "The Barge") which took me on many many trips with an incredible amount of gear. A couple years later I bought a lightweight Cobra Tourer 15' and other than a small combo FF/GPS unit and AA battery pack. Wow, did my enjoyment factor go up! It is easier to paddle through the surf, lighter to load and unload from the truck, and just generally less crap to load up and unload (and wash) afterwards.
My typical kayak equipment consists of:
Yak with rudder and fiberglass composite paddle
In the hatch below deck:
Sm. drybag with fishing license, cell phone, hand held VHF, and snacks
A lanyard with clips is attached to a post under the seat so I can easily reach it while sitting. The dry bag is at the end of the line on the last clip. On the other clips I keep my mask, snorkel, knife, dive watch, gloves, stringer/game bag, and any other small gear I need while diving.
On the foredeck I lash my fins
On both sides of the rear 1/3 of the yak I have mounted bungee "paddle keepers". These hold two guns and a dive flag. The weight belt is usually in the rear tank well, but strapped to some padeyes in case I go over on a wave.
When I dive clear areas without kelp, I attach the butt of my gun to a 50' float line which is attached to the yak and I just pull it along while I hunt. If I'm in thick kelp, I use a SS kelp clip on a 12' section of float line to secure the yak to the kelp stalks.
Either way, I usually just swim my catch back to the yak and drop it in the tankwell so I don't have to drag it around.
My personal favorite yak for diving is the Scupper Pro from Ocean Kayak. If you can get one with two hatches, even better, but most have a bow hatch and a rear tankwell, which has it's advantages as well.
Good luck!
Brent
Water bottle