We're talking about post collapse civilization here.

Lots of people already own that, along with several methods of generating electricity like solar, wind, gas/diesel/natural gas/wood gas generators.

They are if they're busy sustenance farming

It is subsistence farming and your understanding of it is completely wrong. That type of farming is very low effort. People who live like that have a shit load of free time on their hands. The problem for them is they are too poor to afford anything because they don't earn any money from that.

First off that type of farming is done by individuals and family units. In a community one farmer can easily feed everyone especially with modern farm techniques and equipment. And don't start with the claim that the equipment won't work. That is more nonsense from people who never farmed.

Second, militia groups have provisions saved up that will last them years. They are not relying on farming.

Third, the conditions you are imagining during a collapse will not last more than a year or two. Most of those who did not prepare will be dead in 3-6 months. Being prepared to survive for 6 months is enough to get you through it and then adapt to the new environment.

The biggest real threat is a government effort to exterminate people using forced injections like they tried in 2021. The existence of militias made it impossible for the gov to do that quickly and quietly. Engaging the militias would cause a revolution. The militias only need to resist long enough for everyone to realize they are next and start fighting back. That is the real world condition that they need to be prepared for, not some absurd walking dead scenario you made up in your head.

Another real threat is race riots like Detroit had. Once again the survival tactic is being armed and combat ready enough to repell large numbers of poor discipline low IQ thugs who will be subdued within a month, or starve out within a few months. Farming does not play any role in survival. It is all about having provisions and safety.

The rare case of genocide by famine is the only case in which a longer term solution is needed. That will play out far different than a collapse. I don't think it is even possible in the US. It will start with lock downs and a government takeover of farms and food delivery. At which point the militias will know to develop hidden food sources. They will have more than a few years of rations before the normies panic.