Ideas for the campaign?
     If that's what you meant, I would suggest sourcing from Metro: 2033, or Fallout, as examples.

A setting that, depending on which type of disaster caused the collapse, may or may not have caused folks to go underground.  If so, for how long?  Are there different kinds of humanoids now because of generations under the surface?  Subspecies with bonuses to seeing in the dark or evolved to consume less food and still sustain.
     Maybe society doesn't use cash for goods anymore but might utilize bullets as a universal currency.  The different kinds of caliber rounds could be worth more, like how our bills are $1's $5's $10's, and such, and as 9mm is the most common round, so it's less valuable as compared to a 7.62mm for a rifle; maybe 7.62mm are worth $5 - $10 each.  How accessible is ammo? Is a guy with ONE FULL clip very wealthy in these times?  This may impact players' choice to enter into conflict with persuasion rather than expending ammo and literally wasting "money."
     Everyday survival might be a theme.
Survival checks apply to the need for food or water.  Suffering the loss of HP or stats based on how malnourished or dehydrated a player is.
     This is off the top of my head, of course, and mostly gathered from those video games.