I was just brainstorming this the other day. Some other things that I thought of were:
1. dried fruit-- apples, apricots, cherries, raisins, banana chips
2. Fresh fruit or veggies-- baby carrots, apples (you can slice them and put into ziplocks that morning) grapes
3. Sturdy crackers-- wheat thins, goldfish, crunchy granola bars
We LOVE the no spill snack cups we got at Babies R Us. Even for my older DS because you can pack slightly more delicate snacks (like grapes) and they don't get crushed.
I know it seems a little heavy on the fruit and veggies, but my kids eat a lot at home, so when we travel if I don't pay really close attention they don't eat enough fiber and we all suffer for it.