Just start shopping exclusively at the dollar store for groceries. Ramen, canned meats, chili, soups, stews, pastas, tuna, sardines. If it’s really primo, they’ll have a freezer with gas-station type burritos. Add a few energy drinks (make sure you get the cheap ones with extra sugar, like 2/$2) around training, and honeybuns intra for bigger sessions like squatting. Add in some honey bbq Fritos or bags of cheese puffs to fill the (definitely non-existent) caloric gaps, and you’re set.
*DISCLAIMER: you may need supplemental potassium, extra diuretics, blood pressure meds, statins, insulin, and a good can opener.