The start point was cities shut down without food or fuel nor much of anything. Think about the Charlton Heston Movie. The survivors of the city or urban wars having eaten up everything worth eating since without electricity a certain spoilage will have occurred fuel up what they have left and set about raiding the country side. Here people know about making candles and growing then canning and preserving food stocks. They are also armed and many are veterans. As the raiders who for the most part like most city dwellers get lost with three trees and no sky scraper to guide on sort of blunder around looking for the next corner candy and smokes store. when they get lit up for what the country folks need. Tires, some fuel and weapons. One bucket loader and dozer operation they are six feet under.

The fly in the ointment maybe is any military unit had superior weapons and MRE's They leave the city and go to where people know how to grow and preserve food and make a trade. Division of labor. Gas for Grub. Society starts over in areas where society can sustain itself. cities are not included. they have nothing to offer.

The start of all this is the France ISIS situation. But Europe is a mass of cities and town separated by a few farms at least until Poland and "Ukraine.or the old Yugoslavia area Europe being mostly cities and minus on food production has nothing to offer except to mercenary military units.

North America for example is the opposite except in the NE USA and eastern seaboard Lots of mouths, lots of cars, low on food, low on fuel.They have, nothing to offer and assuming their military units head west looking for trades.

Low on the list of useful skills? Politicians, Media, none hard science professors except....some philosophers and historians and the respected non hard science skills.

The first three don't even make the list. Nothing to offer. Add Washington bureaucrats. Unless you need weeds chopped and lettuce harvested. Stoop labor jobs. What else are they good for?