Since I'm (still) a F/A myself, you could say I fly practically on a daily basis. From a pax point of view, I would say the vegetarian lifestyle can be combined with flying, say, once a month, just perfectly.
Aside from the flying activities, you had better make sure you have a varried menu, though. However, getting into that would really
be off topic, I'm afraid. Mind you, there are plenty of good resources on the Net that will provide you with lots of helfpful information on vegetarianism in general.
All the best and fly safely (and veggie