I've been known to pack several different meals based on what I feel like eating.
Lately, I've been packing a pre-cooked/pre-seasoned frozen chicken breast (it's pesto seasoned). Then, I like to dice up a tomato and pack some feta cheese crumbles. After I microwave the chicken breast (I microwave it with the tomatoes so it stays nice and moist), then I add the feta cheese and eat.
Sometimes I'll just pack cottage cheese and beef jerky and snacky foods like that. If I don't have time to pack anything, I usually go to a local grocery store and buy a big tub of greek yogurt.
If I eat out, I usually just run to wendys and get 2 jr bacon cheeseburgers and throw out the buns. That only runs me about $2.50ish.