When people are willing to fight for resources as it will eventually come down to, the size of your group (tribe) and the ability to control your area defenses is the factor that will determine survivability. In a total collapse of civility people will by necessity revert back to the walled fort concept. All through human history this is the only protected method of survival against larger groups. This method is still used today by our troops in Afghanistan when they put up a FOB (Forward Operating Base). Small groups will either join other groups for mutual assistance or be eliminated by aggressors.