What do you do? You go fish. Coast. Streams. Lakes. There’s urban fishing, too. Nutrias. Rats. Crawdads.
Snakes are easy to kill. Slow creatures. City pets, pet stores, and zoos are easy pickings, too.
What you avoid are humans, especially groups of them or someone dug in with supplies. Anyone with a fire and food is a high risk to have tools and weapons, and avoiding being wounded or expending energy fighting is like stocking up with 5 course meals for a couple of months in energy equivalence.
The flip question is how do you behave when you have food that others do not have. Killing “everyone” is a high risk plan, for example...as is “trusting everyone.”
Do you sleep out on a boat on a lake, under an overpass, on top of a skyscraper, out in a field, in a forest, in a bunker, in a house with more windows than you can monitor?
Do you shelter in place or bug out?
Do you yell to a passerby that you will trade a can of food if he chops up firewood for you?
Pure survival is the easy part. With a knife, shoes, a pot, and a fire starter...maybe even less (just a knife for the hard core), boiling water to be safe, catching rainwater, carving spears, and you’ve got the basics.
The hard part is the step above pure survival. Interacting with anyone else, such as trading. Entertainment. New social structures.
Remember Eric Robert Rudolph? He was an expert survivalist. The Feds said he probably never would have been caught if he didn't get lonely.