Not a silly question at all. You will see people carrying just about every kind of bag imaginable from traditional purses, to fanny packs, backpacks, diaper bags, camera bags, and everything in between. I personally have the most success in the parks with a backpack-style bag. I find that I need my hands a lot in the parks for carrying drinks or holding my kids' hands. Backpacks just make this easier for me. I have a mini wallet that I keep my park passes, room key, ID, credit card and a few bills in. I throw this in the backpack with a water bottle, sunscreen, and other items (
see here) and then I'm good to go.
If you find something else works better for you, then that's fine too.
Hope you have a great trip!