Snacks for in-flight: boiled eggs, fruit, crudite's, cheese, crackers, rolls, cookies, pastries, pickles, olives (packed w/o liquid in a plastic container). A couple of water bottles that you emptied before the security station and filled up at the water fountains or with soda at the restaurants. If it's a long flight, skip the soda and go for the water or some other non carbonated beverage; you might need it since the air in the flights is very dry, and you don't want to have to wait for a flight attendant when you want a drink of water.

Other food ideas:

Mornings, get a McMuffin or the like, or pastry at the fast food places outside your gate.

Lunch or dinner time, get a burger and fries, or something more elegant to go. You can carry on about anything if you buy it inside the security check. But get something that isn't particularly difficult to eat.

Then have some sort of snack packed in case you get hungry farther into your trip if it's a long one. I generally don't end up eating the snack foods if I get something at the terminal. Then I have them ready-packed for the return flight. But if you intend to have a real meal to carry onto a shorter flight, don't take perishables as snacks.

One thing...if you carry on a nice meal, it occupies some of that time that's on your hands, whether it's in-flight or waiting for a late flight at the terminal.