For my last trip I packed fruits, a little dish of Kashi cereal and made a sandwich of hummus, onions, tomato and basil. If you have an iPhone or iTouch there's an app called VeganExpress that lists lots of chain restaurants and what their vegan choices are. Some barely have any and some have a surprisingly decent selection so if you're stuck in an airport and need food it's very handy.
I was surprised last time I was in the Atlanta airport and ran across one of those small sandwich stands and found something called 'vegan wrap'. A pre-made vegan wrap? I was shocked to find it and it was good.
Yay! I'm glad VeganExpress is coming in handy for others too :-) I've got Yum Yum too and one called VeganSteven I think. There are a few vegetarian ones that list out vegan friendly places too I believe, I've gotten quite a few apps that are proving very useful.