I used to poach chicken, cut it into bite size pieces and throw it in a plastic bag with a sauce that would be good at room temp -- tomato chutney was a fav for a while, salsa also works. I was comfortable with that at room temp for a couple hours. Apple and orange slices are another fav for eating on planes. In terms of less perishable things, RX bars live in my backpack. Trader Joe's sells single-serving trail mix and single-serving olive packs. If I don't need to worry about food restrictions crossing borders, turkey jerky is a good high-protein go-to.