It depends on how long your flight is if it's going to be a health hazard not to eat.
Never had a problem with eating and flying. Sure, best not to be having a snack on short final but in cruise, no problem. Naturally, if you're in a hot climate don't take food that'll spoil quickly or carry a cooler bag (that's what I did).
Thirst is more of a problem. Take water on all your flights.