Aside from the threat of well-armed and -organized gangs, the other thing we must be concerned about (at least initially) is the potential for large, unorganized, starving hordes of hungry folks. The closer one lives to main thoroughfares and big cities, the worse this danger is. I don't know how to combat this problem.
In "One Second After", they were conveniently located in a geographical area that lent itself to blocking access. That isn't the case in my area.
We were invaded by the starving hordes from the Gulf Coast in Katrina. They overwhelmed the county/community government's support structure and trashed every place they were housed (think Superdome, but worse).
For the next two storms, the locals posted police at the exits off the main highways and told the evacuees who didn't have family in the area to "Keep moving, there's shelters for you in Arkansas." =) May not work next time. FWIW, folks with apparent medical problems were let in, as well, and taken care of...