We were flying back from one of the do's in London one February and the people across the asile about an hour after takeoff got up and got a Harrods bag from the overhead. They had a loaf of bread and a side of smoked salmon which Harrods had cut for them and then vaccum packed back into shape. Little jars of the sauces or whatever they were using, they started pulling off bits and pieses and enjoyed it for hours.
I think our most common travel food is proably whole wheat tortilla wraps, some home cooked sliced roast beef or turkey, some cheese, and some grape tomatoes. Packaged individually they stay fresh for hours and hours, and are eary to assemble. If you want mayo or mustard, virtually every airport shop has bins of them for you inside security.
My other favorite is shrimp, just dump some frozen cooked shrimp into better containers (or wrap the bag a bit) and in a few hours it will thaw into perfect cocktail shrimp. You can even get smaller jars of cocktail sauce if you want.