Buying foods on minimum amounts of funds for months (what to buy?)

Hello, people.

So, I'm currently in the stage of life where I'll most likely have to start living off of very, very little (no saving at the moment).

And for this, I'm looking for the cheapest ways to live off of as little funds as possible, but to be as satiating and even have some protein.

What ways have you found to live to make this work with as little funds as possible, but eating enough meals and (hopefully) enough protein?

I understand that this might not be the lowest poverty line, but it's a significant change for me from being able to buy different foods throughout the month and do OK to a potential downsizing to having to save every penny I have.