While tasty, bagels and cup o noodles are about as nutritious as tissue paper! I would definitely encourage you to find things that provide more nutrition, you need it with your stressful schedule!
All the fruits and vegetables that can easily be carried and consumed raw, prices vary with seasons. Buy what ever you can afford.
Dried nuts, fruits, and beef jerky. While expensive, drink some water with it and they feel far more filling. If you are consuming less, it isn't as expensive in the long run.
I'd strongly suggest figuring out how big of a price difference it would be to buy whole wheat. While the up front cost of bagels is lower, you get more sandwiches from a loaf of bread. May not be that much more expensive?
And a suggestion since you can't have an insulated bag, Freeze it. Yogurt, leftovers that would taste good cold (unless you have access to a microwave), and the macaroni and tuna leftovers suggested above will have a lower risk of forming bacteria before you can eat it. Just toss what ever in the freezer before you go to bed. With having a small space, I probably even try freezing food in a zip lock bag instead of a container.
I don't know where you are in the world, but here in my corner of the world, we have many small grocery stores or fruit & veggie stands that are Asian or Mexican ran, and although the produce doesn't look as pretty as the grocery store, they are half the cost. A bruised apple won't kill you. ;)
