Several things I do:

1. When I have a lengthy flight I try to plan my schedule around eating a suitable meal at the airport not terribly long before takeoff. That minimizes the need for food aboard the plane.

2. If there's no time to sit down for food at the airport, I'll get something to go. At many airports I can rely on finding something decent to carry on-- a tray of Chinese food, a box or two of sushi rolls, a sub sandwich, etc. -- and it usually takes only 5 minutes.

3. If I need extra food for a long flight, or I'm concerned that there will be nothing suitable to buy, I'll throw a few energy bars into my bag. I'm partial to the Luna brand. I usually have a stash of them at home as I carry them when I'm hiking.

4. Energy bars do get boring after a while, so if I'm looking to go hard-core self sufficient I'll bring salami, crackers or bread, and cheese.