Little debbies. Large box.
*Roughly a dime for every 100 calories. Can literally feed yourself for a dollar a day if you can tolerate eating the same cake.
-More to the point, is good filler of calories so you don't go utter zombie-mode in school. You'll still want to eat proper food at least once a week to prevent scurvy.

Add butter or a greasy hot-dog to ramen-noodles, will taste *far* more filling. And learn to boil an egg (because you *NEED* a protein-intake).
-Rice is a 2:1 volume-ratio of water to dry rice (add butter to add flavor and cook faster).
*If butter is a freebie-condiment, TAKE IT.

As a last resort, coffee-grounds will suppress apatite.

Also, invest in a snow-shovel, a wide one for running like a human snowplow on light dustings, and a narrow one for when you get a wet dump. Start shoveling driveways for $10/ea this winter and you may be able to afford a hot meal every other day.
-Seriously, hot chow is up there with a dry pair of socks after a wet day of walking (which BTW, can be dried by placing the socks under the neck collar on long marches [or when shoveling snow, place under scarf]).

This knowledge comes somewhat from what I learned about 1940's era combat-rations. Other bits came from talking to some really old folks from the civil war and from personal experience.
-Did I mention that wearing a second long sleeve shirt, scarf, and hat will probably keep you far warmer than a winter jacket on its own?

*Learn a skill/trade and be willing to do stuff older and 'more productive' people aren't willing to or outright cannot do.
-One way to strike-up business is to do it for free the first time, to get their attention. And be willing to simply trade favors (will work for food).
My local community is really in favor of non-taxable barter for services.

Oh, and one more thing, welcome to the job-market.