If some sort of collapse or doomsday happens, one of the possible scenarios is that gangs could take over the cities.
The gangs will start off from their blocks and slowly take over other neighborhoods. People would join them because they will desperately need food and water.
It has to be noted that gangs are already ruling the underground of cities. After a collapse, they will come to the surface in order to claim the above territory. Law enforcement officers will cease to do their jobs out in the open because they will be defending their own family and property.
Everyone will be at risk from these gangs. People should be aware that these angry mobs are even today armed and dangerous.
People living in the cities or in neat suburbs are unaware of the gang activity, line of business and imposing threat to society. People are too busy to even look around and observe all those suspicious looking people in the shadows.
People should take this possibility seriously and prepare for the inevitable. It is advisable to carefully plan how you will defend yourself when a foraging gang of 50 members come knocking at your door. Also, direct confrontation must be avoided.
The only advice is to move somewhere else.
Hopefully, this scenario will never happen.