My neighborhood had armed people patroling their own homes and neighbors looking out for each other.
A whole block of homeowners with rifles watching each others homes is the way to go.
it seems that there are two ways of looking at it, just like short-term survival vs. primitive living. are you holding out until quick rescue from big brother, and how long will that take? or are you figuring on holding out, maybe indefinitely, until some sort of order is imposed or otherwise establishes itself?
the image that came to mind was that of the Korean(?) business owners in the LA riots that protected their businesses. it seemed from the video i saw that nothing moved in their territory that wasn't shot at. they protected their own, but did not appear to distinguish between evacuees and looters. (if i'm wrong, blame the media for selective presentation.)
i witnessed a similar thing in Kuwait City years ago. 'citizens' formed roadblocks to stop & check traffic passing through, sometimes on nearby roads, not just inside the neighborhoods. my impression was that most made it through, but that some didn't. and no one got through (except us, sometimes by overt threat of force) without being hassled and searched. 'contraband' was 'seized', and contraband sometimes included water. anyone with stuff was a target because there were so many without stuff.
i didn't blame them. they were trying to get by and often were providing for families. but i recognized the danger. they were the ones who ignored warnings or couldn't leave ahead of time. didn't matter, they were where they were. and they dealt with it.
nighttime, though, was the time of much chaos. many people had to simply barricade themselves in their homes and sometimes had to defend themselves. i heard stories from some who lacked the capacity to defend themselves against aggression - mostly women and children without defenders, as you can imagine. daytime was the time for travel to obtain life supporting resources for them, but cautiously, without obvious weaponry or stuff. either brought attention. we were about the only ones with both, and we were often resented for that fact alone.
neighbors turned on neighbors, and old grudges were settled in a variety of ways.
as an amateur student of behavior, it was interesting. i don't think my observations were unique and i believe that these types of behaviors are universal. initially friendly and helpful peoples will transition when resources dry up. i didn't make it to the aftermath of Katrina, but wondered how it compared. especially the early days. those of my friends who did have some interesting tales, some never to be spoken of again.
even the mildest have the capacity to become vicious. and those already vicious...