We bring beef or turkey jerky for extended flights, and trail mix or
Kind bars or granola bars. For shorter flights we usually take sandwiches on a bagel or toasted bagel -- bagels tend to hold up better than bread -- baguettes are also a good option. Another favorite for us is pizza. We happen to like cold pizza smileys/smile.gif and since the night before a trip is often busy with packing and last minute departure agendas it's easy to order a pizza for a quick no-fuss dinner and have leftovers for the next day's flight.
Salads are also good. I like to stop at Trader Joes the day before a flight and grab their ready-made salads (they have some really delicious ones that run around $4 each), some turkey or beef jerky, big bag of mixed nuts or trail mix and a few Kind or Larabars...one stop shopping and costs alot less than food at the airport or on a flight. Keep in mind though that anything with cheese or meat or protein needs to be consumed within 4 hours of being removed from your refrigerator, for food safety reasons.
Peanut butter and jelly sandwiches hold up well too but I'd probably opt for almond butter instead of peanut because some folks are highly allergic to peanuts. We were on a Southwest Airlines flight last year where they apologized for not serving peanuts because a passenger on board was so allergic it would send them into anaphylactic shock, so the flight attendant also asked that anyone who may have brought peanut butter or peanuts on board to please not open up or consume those items.
I've seen others bring ramen noodle cups, oatmeal cups and instant soups and ask for hot water on the flight. Sushi or California rolls seem to be popular too.