First, 1 per family, or multiple in the family?
After reading the Standing in Line thread, my mind is churning.
Water bottle(s)
Sunscreen
Camera, phone
Charging cable and battery charger
Now add: book, notebook, simple game...
if you are taking both a camera and phone - unless you are on your phone ALL DAY - you shouldn't need a charger for one day. And a book, notebook, and game? No way I would carry those - too much weight.
Here's what I take for the day:
Travel size sunscreen (they are a $1 at Target) (put sunscreen on before leaving room/car)
A ziploc bag with a piece of dental floss, ibuprofen, if I already have a cut - a fresh band-aid, or if sick, other medicines
Lip balm
Phone
ID, credit card, health insurance card, Annual Pass in a flat card holder (note - not my normal wallet from my purse)
If driving - keys, car insurance card
Mini-comb
Camera - if I'm taking it that day
Maybe an extra water bottle
We don't do autograph books anymore - but we used to carry those with a couple pens
Definitely ONE per family unless you have a kid that wants to carry their own bag ALL DAY. Don't be a packhorse for a kid. If you are concerned about needing a change of clothes, changes of shoes, etc - we might bring a bag that we check in a locker.