We all (kids too if you want to bring LOTS of snacks!

)wear fanny packs and put a juice box, granola bars, baggies with: chips, trail mix, raisins or pretzels; cheese sticks (eat within an hour or two) and that type of thing.
Other things I have brought are individual applesauces and individual fruit cups, or an apple.
You can make the trail mix very inexpensively (this was my kids' favorite snack to bring in their fanny pack in a zippered snack bag). Just throw together some M&M's (or Wal-mart has "choco buttons" that I don't like as well as M&M's by themselves, but PREFER to M&M's in trail mix), a few marshmallows, raisins, and peanuts or granola.
YUMMMMM!
I also have a "platypus bottle" which I bought at Gander Mountain (sportsmans store). It's flat with a water bottle spout. It's sort of like a baggie only heavier weight plastic. It folds in half and fits great in a fanny pack. We just fill it at a fountain.
It costs a fortune to eat at the parks, so this saves us a ton of money. You can even fit a sandwich in a fanny pack! A lot of people had backpacks, but I like the fanny packs because you don't even have to take them off for rides, etc.
Just to give you an idea of everything that fits in a fanny pack, here's what I had in mine last week at Universal studios:
2 fruit and grain bars
1 snackwell candy bar
1 weight watchers 2 points bar
about 10 hard candies (creme savers, etc.)
1 baggie of pretzel sticks
1 (1 serving)package of Milano cookies
1 (1 serving) package of Sun Chips
1 platypus bottle
1 package gum
1 bottle of eye drops
1 pair sunglasses
checkbook register
Weight watcher's spiral food journal
weight watcher's slide rule
1 chapstick
1 lipstick
1 mascara
1 eyeglass cloth
1 nail clippers
1 emory board
money
6-8 cards (Visa, ATM, DL, etc.)
folding portable scissors
3-4 bandaids
4 packets of splenda
2 kleenex
1 travel size bottle of tylenol
2 pens
2 keys
1 disposable Kodak camera
(I don't think I forgot anything!)
(DH keeps his wallet and a few other things in his)
My fanny pack has 1 large pocket and one more pocket out front that I keep the pens, money, gum, and credit cards in. Plus a very small pocket in front of that pocket that I keep the splenda, chapstick and nail clippers in. It is an "average" sized fanny pack -- not large. The extra pockets are the secret, I think, so look for one that has more than one pocket for you.
Kids just need a basic one with room for a juice box, sandwich and granola bar and/or applesauce.
This probably too long, but hope you have a great trip!