You should ask your charter what they are going to provide (license, fishing gear, bait?), like this info from a local boat:
Q: What do I need to bring with me?
A: Nothing. We provide you with a rod, reel, bait and tackle. You can buy hot fresh cooked food, beer, soda and snacks from the galley. We do recommend you bring the following. Sunscreen, sunglasses, visor or hat.
http://www.pastimeprincess.com/FAQ.htm
Since the water temp will be in the high 80's (one of the reasons hurricaes form at that time of year) then I don't know if I'd bother with a windbreaker unless the weather is bad, you are going to be out late or you are already so sunburned you can't stand any more sun (been there, done that

)
My DH adds you should bring a camera and a cooler if you plan on keeping your catch. And just me, but I would say be sure and take some Bonine for sea sickness before you go, because if you get sick the trip will seem endless and no fun.