I don't use a lunch bag, but I have a kind of plastic lunch box that I always use. I'd suggest finding one of those, or one of those big sets of various sizes of containers so that you don't need to throw out baggies all the time. Anyway, here's what I eat.
-tortilla/s, cut into pieces and eaten with a mix of beans, cheese, and salsa
-whole wheat pasta
-beans (rinse them off before you put them in to avoid the goop from the can)
-tofu, fried until crisp, usually eaten with rice and/or cheese so that it doesn't taste so sad unheated
-tofu scramble (see below)
-fruit and cheese (see below)
-carrots (baby or cut up from whole)
-tofu scramble with bell pepper, onion, garlic, grated carrots, and mushrooms; you can really just throw in whatever vegetables you have, and it will probably taste good.
-apple slices, or a whole apple with a napkin on-hand
-fruit and cheese (if you have access to a fridge, or if you just don't mind that the cheese will be warm. I suggest green grapes and apples with sharp cheddar)
-melon, cut up into bite sized pieces
-mixed veggies, usually from a frozen bag--cooked the night before and drained slightly
I always make my lunch the night before, with some time for hot things to cool before putting them in plastic. You can always throw in dinner leftovers, too. You should make sure that containers are watertight, or just be careful to keep your lunch upright throughout the day.