Being in a city doesn't guarantee that survival will be easier for anyone, if compared to what has to be done in the wilderness: on the contrary, cities and urban areas present their own problems and oddly enough, their inhabitants are often very ill prepared to deal with emergencies.
Archaeologists and historians generally think that the first human
settlements that could be called towns and the primitive organization of
society evolved as consequences of common needs like gaining protection
against natural and man-made threats. In ancient Mesopotamia, people
began gathering in towns to defend themselves against raiders coming
from northern mountains - what we know today as Kurdistan -; these
raiders who came from a region that is rather poor in resources and
certainly ore hostile than the fertile plains around the rivers
Euphrates and Tigris, became a real problem and so, it was only a matter
of time until people agreed on pooling their resources, probably under
the auspices of some of those mountain raiders that then formed the core
of the first organised armies or defence forces.
It wasn't just a
matter of money: As raiders took the produce of each harvest the robbed
farmers were often left with no thing to eat until they could harvest
again, and that took months. Survival was a complicated thing to achieve
without those cereals and at any rate, attackers could come and steal
again, so protection for food was as important as protection for people.
There was no contention for those that lost their harvests either by
natural catastrophes or by the action of men because the productivity of
those early agricultural ventures was nominal if compared to today's
People could harvest about what they could store and eat
between each harvesting period, so helping your neighbours wasn't often
an option, even if you knew that helping them would in the end serve as
an insurance for you, expecting the same treating in the future.
How does this apply to a modern urban survival scenary? Well... things have not changed much in this particular realm.