An excellent form of this being chickens – and ducks, which I just got five more of. Including two male Muscovy and three female Muscovy ducks, which renew themselves without any work needed on my part. The ducks not only renew themselves, they renew my supply of duck eggs – which are superlative for baking and highly desired by others for that purpose.
If you have them, you not only have a renewable source of food, you have fungible food. Duck eggs can be sold – or traded – and are often sold for more than chicken eggs because they are harder to get.
Free-range chicken eggs are also desirable, fungible and renewable. My small flock of seven girls provide that many eggs per day and sometimes more. Which is more than enough to feed two people heartily (scrambled/over-easy/hard-boiled eggs as such plus eggs added to rice or beans to make a protein-rich feast) and leave enough to sell or barter to others for needful things in addition to food.
Or other kinds of food, such as beef or pork – which is harder and more expensive to raise and not feasible to raise unless you have at least a few acres of land. If you have a back yard, you can raise chickens – or ducks.