Being raised in the southwest, priorities for survival were always crystal clear. You have to have water, and you have to have electricity. But beyond that, everything is negotiable. And that is a good philosophy to have in a survival situation, because the idea of living “as an island” has some serious flaws.
I am dubious about home gardening in most circumstances, because except under very strict limits, it cannot support you. Fortunately, in most of the US people can raise potatoes, but that is one of the few plants that can provide substantial nutrition in a small crop area, and with limited fertilizer, pesticide, and protection from birds and animals.
Were there to be such a catastrophe that most people would have to leave the southwest, it would be wise to leave with them.
There is a functional limit to how much society can collapse if there are people still around. Collectively people have enormous resources in the US, and are practiced in organizing for mutual benefit.
You surely don’t have to have electricity, my family didn’t have it until I was 12 years old and we survived just fine, as did whole civilizations before us. A short term plan should include a generator to save food in fridge and freezer, but for long term you better plan on not having electricity unless you have everything it takes to create it- fuel for a generator will be limited in worse case scenerio. You of course need water. If things fall apart so badly that basic survival is the issue, then survival will be the number one concern and will consume nearly all of everyone’s time. The main thing we are talking about is survival here, not having everything we have now. Survival consists of hunting, gathering, and a large garden and domestic livestock such as chickens, milk cow, etc. can supplement that. It is not the same as my little garden that I piddle with some years when I could get by just fine without it.
Why do you think what I suggested is “island” planning? Of course like minded folks will work together as they have throughout history. Having a little of everything makes sense because what you can’t use you can share or trade for what you need. Everyone is in a different situation of course, but many do have the means to have garden and livestock. Many of those that don’t have relatives and friends that do. Some will need different plans if they live in the city and so do all their friends and family, they will have to have things and of course their labor to trade.
Many people survived in the Southwest before all the modern conveniences, it surely can be done. It will be tough anywhere if things are that messed up.
My family lived in the midwest during “the” depression. Large large garden, grew, dried, canned, ate very well. We did not have a cow but we had chickens, guinias, geese, ducks, and often rabbits. We also had a “storm cellar” otherwise known as a root cellar. There we stored potatoes etc. Can be done.