It's actually much easier to tell you what you can't bring into the theme parks. These are the items that are NOT permitted in the parks:
Guests are not permitted to pull items behind them. Any item that
requires a Guest to pull it behind them, including a stroller, is not
permitted into Disney Parks. Other items that may not be brought into
Disney Parks include, but are not limited to:
- Items with wheels, such as wagons, skateboards, scooters,
inline skates, shoes with built-in wheels, two-wheeled or three-wheeled
conveyances, strollers larger than 36 inches x 52 inches, suitcases,
coolers, or backpacks with or without wheels larger than 24 inches long
x 15 inches wide x 18 inches high (coolers required for medication may
be stored in a locker or at Guest Relations), and any trailer-like
object that is pushed or towed by an Electric Convenience Vehicle
(ECV), wheelchair or stroller
- Alcoholic beverages
- Weapons of any kind
- Folding chairs
- Glass containers excluding baby food jars and perfume bottles)
- Pets (unless they are service animals)
- In Disney's Animal Kingdom theme Park (for the safety of the wildlife), balloons, straws and drink lids are not permitted.
Other than that, you're good to go. On a typical visit to WDW, I carry with me snacks, water bottles, sunscreen, ID, camera equipment, sunglasses, rain gear, guide books, etc.
Hope that helps.