Our typically backpack includes...
diapers, wipes, tiny tube of aquaphor, a few cars (for DS to play with at restaurants), one light up toy, smaller camera (big camera is in it's own bag/around my neck), sunscreen, few snacks, disposable rain ponchos (3 or 4)....
Um, that's all i can think of right now. Though I really need to start getting it all together in one place. We leave in 6 days!!
We typically keep all our id, money, park ticket stuff in our pockets.