Our family of four use fannypacks. My husband and I have fannypacks with a medium sized main pocket where we put our small camera, first aid supplies, snacks, and rain poncho; an organizer pocket in front for money, change, credit cards; a small zippered pocket at left hip (part of the belt) for cell phone; and another small zippered pocket at right hip for passes. Our boys (ages 10 and 7) have smallish fannypacks for their wallet, snacks, rain poncho, and clear cosmetic bag for lanyard and pins. I usually have a water bottle on a strap too.
Fannypacks are great because you don't need to take them off to get on rides. I like somewhere convenient for my passes, since we are always getting them out to put in fastpass machines. Because the cell phone is not buried in my bag, I can feel it when it vibrates....the parks are so loud, I can rarely hear it ring.
My boys fill their fannypacks with snacks each morning and eat all day. They still eat a good lunch too. Snack items include: juice boxes, beef jerky, small Pringle packs, drinkable yogurt (Danimals), trail mix, etc. Their packs get emptier as the day goes by.
We have enough room in the packs to stow our sunglasses and hats while on rides as well.