Besides the standard grain/starch foods that travel well, maybe try these:
Sliced apples - You can slice your own and then toss them with a tablespoon of lemon juice or lime juice or diet sprite (the citric acid, the stuff that makes the lemon/lime juice naturally tart, will prevent browning). Or you can buy pre-sliced apples.
Dried fruit like apricots or prunes (not raisins or very small things like that if he's little--they are a choking hazard). These are semi-soft, so if he has teeth, he can easily tear them into bite size portions.
Apple sauce cups - either buy the indiv. servings multi-packs, or make your own with reusable containers and a large jar of applesauce. The multi-packs offer lots of variety of blends (we buy Musselman's natural, w/o any added sugar, and I think there is another brand that also does that).
Carrots - either baby carrots or the pre-sliced or pre-shredded ones (the shredded ones are messier bec. the kids drop them, but they might be easier to eat).
We also still sometimes buy the freeze-dried fruit snacks in the baby food section, or order it online, since it keeps a long time.
If you have access to a small cooler and can throw in an ice pack, your options can expand to include:
cheese (we like the portability of string cheese)
yogurt
lunch meat
mini-sandwiches
hummus and crackers or pita to dip
frozen apple sauce (good for if it's hot! :) A lot like a popsicle, but has the fiber of the apple pulp)