There's so much truth to all these replies, even the joking ones. Here's what I've learned over my 10 years kayak fishing. Your 11.5 may be short for bigger water especially salt, be careful in high wind and waves. Wind sucks.
1. Start simple, keep gear to a minimum and learn what works and what doesn't. this also helps a new comer when they dump in the water (keeps gear loss to a min
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2. Start small, small lakes or real slow moving river
3. Get proper sized paddle, for a SOT with 33"beam an adjustable 230-255 is best. To short will result in early fatigue.
4. Buy a fishing PFD to keep the small gear secure and for quick access, pliers, forceps, snap swivels, line nippers.
5. When fishing in cold weather buy dry paddle pants because you will get soaked
6. Not a requirement for all but I find that a rudder is a great addition to a fishing kayak because you can control your direction in most cases when hands are tied up with fishing rod.
7. When approaching your cast point, slow down well before and gently stop kayak with paddle, early on you will find that you run over where you are fishing before you can get a cast or two because of momentum.
8. Practice self rescue. Now this is something that I haven't done myself and with 10 years experience I know that I am due for an unexpected swim one of these days. Go to a boat launch (not during busy time) walk yourself out and practice self rescue, learn what works with your SOT, paddle float, rescue rope (used as a foot step) etc.
9. Don't forget to enjoy yourself.
10(late addition). Don't be afraid to trim down the handles on your fishing rods. When wearing a PFD larger rod handles will hit the vest causing you to have to hold the rod out further resulting in early fatigue. My ultra light and medium rods the handles were fine but my med-heavy rod I trimmed about 2 inches off of the butt section. But again start simple and learn what works and what doesnt for you.
Salt water
Flag kit
Marine Radio
Flare to shoot at boats passing too close, or spare rod with 20ounce weight on it.
Paddle partner
Do not go out in ocean until you are able to paddle 75% power for 30-45mins without break. Endurance is very important. Tides, wind, waves.