Remember that the gangs are just a small part of the problem in a SHTF, the government in a total collapse will take over all food supplies. They will not care much about the cities.
Great history examples of this is Russia and Cuba. In Cuba they went out to all the farms and took control of all food production. What happen next is food production went down since the farmers were not interested in working there farms for only enough food for there families. All the rest of the food production by the farmers had to be turned over to the government. This is how it works in a SHTF, ether a Dictatorship or Communism take over which the two are the same! What do you think the FEMA camps are for? They are not for just the city people, they are for everyone that doesn’t like what the government tells them to do and that will include any farmers. There will be a war in the farmland because of this.
The farmers are all conservative that believe in the Constitution. That has always been the enemy of the government, The cities are all full of left wing groups(more in the north) which the government likes.
That is what I see from all the history of all wars, governments take over food supplies. Cities don’t have any food supplies so they are not interested in them. They just let the cities burn up them self’s.