There are things in life you never want to put in your mouth: your foot, dirt, electrical cords, and airline food. The latter, airline food, is something some people don't have to worry about anymore. Many flights no longer serve full meals and instead hand out a bag of crackers and a soda the size of a shot glass. This lack of food might be better than handing out an entire airline meal. Unless you're sitting in first class, an airline meal is sure to sit in your stomach like a rock.
With the lack of food, or at least the lack of edible food, airplanes are often things that allow hunger to take flight. This leaves people helpless. Getting up and going to a diner or a cafeteria isn't exactly feasible. For this reason, it's important to take snacks on your flight that will leave you satisfied without contributing to jet lag or airsickness.
Candy: Yes, candy may go against everything you've ever read in the brochures at your doctor and dentist office, but candy is a great airline food. Not only is it easy to transport, but it also helps to hold you over as you go from point A to point B. The chewing motion most candy requires can also help to keep your ears from becoming uncomfortably clogged as altitude increases.
Trail Mix or Dried Fruit: It's healthy, it's easy to carry, and it's satisfying. Taking a bag of trail mix or dried fruit on a plane is a great way to snack without feeling guilty. It's also a great thing to bring along if you have kids. It will keep them busy while forcing them to eat well. However, because salt can contribute to jet lag, it's a good idea to purchase unsalted or low-sodium trail mix.