I always pack granola bars and peanut butter cracker packs. Its more a diabetes thing than anything else. If my blood sugar crashes while we are stuck on the taxiway or sitting at the gate in a delay I can address it without having a FA intervention.

My suitcase always has some too since time zones mess up my sugar control and I will sometimes crash at 3 AM at a hotel and wake up and eat a snack. It's sometimes tough to find a 'quicky mart' type place, especially in a downtown area. So, I've learned to bring snacks.
Belvita bars, granola bars, Kind bars, etc. Easy to carry. I get the ones without chocolate so they won't melt. Surprisingly filling and somewhat healthy.

I have to remind myself to eat them all so I don't accidentally enter the country without declaring the snacks, get caught and lose my GE status.