Sacred Haven of Debauchery

And there's the classic question: what can you eat for around 50 rubles that's both a little and filling?

If you cook:
Rice, any kind of pasta, dumplings, potatoes (although they're usually more expensive), cottage cheese for syrniki (cottage cheese pancakes).
If you don't cook:
Find something at a fast-food place, you used to be able to buy shawarma, but it's gotten more expensive now. Instant noodles, Rolton, ready-made salads are more expensive (or rather, you won't get full for 100 rubles), buns, pies, pancakes.

Added 1 minute later
By the way, I remembered a story by Zadornov about 1 egg in the refrigerator:)

Oh, and by the way! You can buy quite a lot of zucchini for 50 rubles, and then you can stew it in water or fry it.