Hey welcome to the site. As it was already mentioned, do a search in the kayak fishing forum for the information as you certainly not the first person to post on that subject. Lots and lots of things that are common sense to have and others are for your comfort. I am fairly new to kayak fishing as well and here are the things you should definitely have for any body of water:
Fishing license, whistle, a good PFD, paddle with leash, first aid kit, a set of dry clothes in a dry bag, & toilet paper (in ziplock bag).
Some would add these things: anchor trolley, anchor w/float, stake out poles, milk crate for mounting and holding your tackle/cooler, fish finder, marker flag.
It also really depends on the type of fishing but it's always best to be prepared to flip you kayak rather than wishing you had planned after you went into the water.
Be sure to follow this link and go through the first post regarding fishing kayak setups
http://www.ncangler.com/forums/forums/56-Kayak-Fishing
It's all a personal choice on how simple or how elaborate you wish your fishing machine to be. Good luck!
John