I imagine in a really long haul disaster, it would really depend on the nature of the local community and your distance from society. If the local authorities want to impose order and redistribute your resources, a single person with a gun (I assume that’s what you mean) wouldn’t realistically be sufficient defense.

If you are far enough out and might only have to scare off, like, an occasional random drifter, that’s another story.

Or maybe you mean they should invest in their community and social network. Being seen as a local or at least familiar, and having a good reputation in the community seems like a really useful thing in this sort of scenario.