These are items we've used at Disney and elsewhere over the years for a quick snack or meal on the go:
Granola Bars
Beef Jerky (we make our own, much cheaper and my boys love it)
Trail Mix (I love those large bags from
WalMart but you could make your own.)
Celery and PB
Baby Carrots and Ranch Dip
Apples, Grapes or Cuties (less mess with these oranges)
Goldfish Crackers, Pretzels, Chips, Cheese Crackers, any snack pack really.
PB&J
Deli Sandwiches
Cheese Sticks
Gogurt (those yogurt tubes - they're just as good frozen)
Cookies
Flavor Packets and a water bottle. Make your own koolaid or lemonaid.