It is always possible, locally, to return to use of animal dung fertilizer, crop rotation with legumes, etc.  Won't support high population density but might not have to. Hell, I grew up milking a cow, letting most of the milk curdle and feed to the pig, keeping a few chickens and tending a large garden.  We have a working well on the property in case city water becomes problematic or too expensive for irrigation.  I didn't expect things to go to hell as fast as they have, but the wife did, (on totally other grounds.)  

Best of all, I don't need to drive much, and can still ride a bike if need be. I have always kinda dismissed the survivalists, but now....

As the Dutch said while fighting the Spanish: "It is not necessary to have hope in order to persevere."