Just random things you can put in, not necessarily all of these items. Since it won't stay cold:
-fruit cup (non refrigerated kind)
-any kind of snacks really (combos, gardettos, cheeze its, goldfish
-beef jerky (they have these "lunchable" type things with jerky, pretzels and cheese
-the nutella on the go packs
ETA: and of course something to drink, anything but milk.