For a likely scenario I would consider what happened in Russia in the years following the revolution. The country was in disarray due to the aftermath of WW1, and they were also under embargo from the major powers who were also backing the "White Russian" forces in their counter-revolutionary civil war.
The populations in the cities were starving, and the ruling communist party knew that they had better be fed or they would lose control of the situation, so they dispatched commissars with militia units to the rural areas to sieze food supplies from the peasants and "kulaks"(larger landowning farmers)who, of course were vilified as "counter-revolutionaries" in order to justify the appropriation of their goods. As a result of this many of the rural workers and experienced and knowledgable agriculturalists starved- guess what that did to the food supply?
I suppose what I am saying is that, in this sort of a crisis, the government is more dangerous to you than random pilagers if you had the foresight to produce enough food to keep yourself and your family (which we do).
Provision needs to be made to enable the movement of significant numbers of urban workers to be billeted in areas capable of food production- ideally with friends and relatives at first. Surveys need to be done to determine which areas of the country best produce the foodstuffs we mainly import (principally grains) which shouldn't be too difficut as NZ was self-sufficient in grains until the 1970's.
The political parties will never address these issues as political power lies principally in the cities. City dwellers would be horrified by what I am suggesting (I can hear the cries of "Pol Pot" as I write) but how many of them have ever actually experienced an empty belly? Many city dwellers produce "wealth" on paper but in a crisis their efforts become completely nullified as they create no tangible benefit with respect to peoples immediate needs. In the longest term I would expect to see a reduction of urban population to between 10 and 30% of total population. I sincerely believe every one of us needs to develop three skill sets to survive and thrive- as a food producer, as a craftsperson, and a cultural / artistic component too.