I'm running an RPG campaign (using Fantasy Age rules) in a medieval setting, a few generations after a sort of apocalypse happened. The region the characters are in is the one that was least affected by it, so everyone who could manage to get there did so, leading to overpopulation. The region has an unnatural though not infinite food production and plenty of drinkable water and mineral resources, but what they manage to produce is not enough to generate surplus. Also, since other communities lie far away across a barren, dangerous land, the possibilities of trade are close to zero. Magic exists in this world and it's uncommon though not rare, but it has many potential dangers and drawbacks. There are many dangerous creatures and marauders about, so a good measure of their resources go to maintaining a powerful military organization.
Would a place like this have any use for coin? If so, would they keep on producing coin, or would they only use the coin they already had (thus probably increasing it's value)?
How would their internal market work? What sort of products would be available?
How would people who do not own land manage to make a living? Hunting outside the communities is possible but dangerous and there isn't a whole lot of prey available.