When the SHTF, it will be worldwide. Food will be a primary problem for almost everyone for months or years. Subsistence living will be the only way to survive long term. Yet, there are probably few areas left in the USA where that is possible, especially as millions of people will be trying to do the same thing in the same limited areas.
It may surprise people to know that there are places where it is almost impossible to starve.
Take Costa Rica. Numerous fruits & vegetables grow wild. The fruit rots on the ground in places. The soil is so rich that a green stick jammed into the ground becomes a tree. There is plenty of game & fish for the taking.
Much of tropical Central & South America is like this - tropical islands in the Caribbean, too. The USA, not so much.
When the SHTF, millions in the US will starve or die trying to feed themselves & their families. City dwellers are doomed. That’s not nearly as likely in a place where you can gather food in your back yard.
I’m just saying...
You might be surprised then that some people are already living that lifestyle.
/johnny
Those with backyard gardens will have them stripped bare unless they have a goodly number of sentries. However, if you have enough sentries, then your little backyard garden isn't going be large enough to feed them all.