Batteries. We take extras for gameboys, walkman, walkie talkies, mp3 players, cameras. They are very costly at the parks and small to carry from home.
Sunscreen. Again expensive at the parks.
Good shoes and provisions for blisters.
Swim suit for everyone. (Even Mom) That pool in the hotel always looks pretty good after a long morning or afternoon at the parks. (We come home midday to relax and swim or sleep)
Cameras. Film (more than you think you could use. It's small and cheaper at home.)
Large barrel pens for character autographs. Notebooks from home for a less expensive autograph book.
Fanny packs. Water bottle with strap. This is all we carry. We take a back pack with a change of clothes for everyone so if the water rides soak you, a change is nearby to slip into without leaving the park. The backpack is put into a locker and left for most of the day. So nice to not tote around heavy items.
Chap stick. That sun is brutal on lips.
Beach Towels. I hate little hotel towels while at the pool.
Guide book. Bring it at least to the hotel for evening reading, if not to the park itself.
PS numbers.
Stuff for kids to do on plane, in car, bus, taxi, shuttle. I print off color pages and bring colored pencils along with Gameboys. Younger kids get a kick out of a small bottle of bubbles. They will bring other kids over in the airport. Maybe your child will make a friend for the plane ride
One place for all important docs. Airline tickets, Disney tickets, shuttle vouchers, PS #s, rental car info, ect. I use a small plastic file expander. Got it cheap at Office Depot.
Travelers checks and cash. It's Disney you'll need it.
Credit cards.
Rewards card from your Disney Visa purchases.
Light jacket for evenings.
Tylenol, Advil, Antacid- in adult and kid strenghths. I take the travel size ones in my fanny back just incase.
Hope this helps