I've been a vegan for 25 years or so. My basic menu on tour is:
Morning: Muesli with soja milk or apple juice,
During the day: Peanut butter sandwiches, Bananas or other fresh fruit, Trail mix or peanuts, Orange juice
Evening. Rice and a tin of beans, olive oil and tabasco.
If I find somewhere that sells tofu, or texturised soja protein, then that gets to be a luxury meal. Pasta occasionally...
I eat this day in, and day out on tour, for months on end. Cheap and nutritious. I think I could live on it forever
edit: I cook on a mini trangia, and eat out of the pot.
Also Vegan.... I second the above... I'd add Humus since you can get it as just about any mid sized store these days. I tend to do lots of pasta while on tour as well.
Also, if a town has a taco bell i grab a 7 layer with 2 missing(cheese and sour cream)... when I just want to be lazy.