When we are traveling, we are inevitably out and about during snack times. Since are children are still pretty young, snacks are still important. Not wanting to spend a fortune on buying something while we are out (at least all the time), especially since Europe is so expensive, we came up with snack packs.
Each of our older children (ages 3 and 5) has their own hip pocket (very retro I know). They get a small water bottle (about 8 ounces with a sport cap), a packet of Kool-Aid to go, and several snack options. You can use anything portable, like fruit snacks, fruit leather, individual packages of crackers or cookies, or you can make your own little packets using snack sized ziploc bags.
This idea has worked out well. The kids have snacks, which they can access at their leisure, and we don't have to carry them!