How many acres would a person need to go feral?

[excessive]

Suppose you were to find a crop worthy plant or meat suitable critter already growing or living on said acreage. Would you be able to propagate native flora and raise native fauna?

I'm thinking a Robinson Crusoe scenario. Say you want to cage a few squirrels or bunnies, or plant a few apple trees? What if you came across, let's say, a medicinal plant (wink, wink, nod, nod), would it be okay to start a pharmacological grow? Asking for a friend.