My backpack has 3 pouches -- main pouch, med. pouch on front and a smaller pouch. Here's what we carry in each:
Lg. pouch - bathing suit for ds (to play in water areas) in ziplock, ponchos, 2 sm. umbrellas, dry washcloth in ziplock, bottle of water, film in baggie, sunscreen and spare t-shirt and shorts for ds.
Med. pouch - autograph book, pen, camera
Sm. pouch - candy, liquid bandaids & moleskin, motrin/tylenol, loose change, tissues, lip balm
In a small, decorative change purse type thing around my neck: id, cash and passes.