you don't need much, make sure to take alot of money! because everything at disney world is over priced. if you don't want to buy water at the park i suggest you take your own bottle. a camera because you'll need something to capture the memories and that's really all you need. i live a couple hours away from disney world and every time i've gone that's really been the only thing i need there. you don't want to take too much because then your going to have to worry about your things whenever you get on and off a ride.
Things you will find that you want will be
chapstick
sunscreen
hand sanitizer (because you won't always be able to hit the bathroom before you eat something)
a camera
cell phone
a small wallet ( don't put all of your money in it, I always carry some in my pocket)
space to put sunglasses (because most of the rides will make you remove them)
same goes for a hat if you are wearing one
a couple of bandages for blisters (just because you never know)
if you have room carry a couple of bottles of water and a small snack (granola bars, jerky )
gum or mints
have fun