In a town, there is usually at least one rich person.
Or a conglomeration of store owners.

I would hope that they set this up before things got bad, or depressioney

And internet might get scarce, but a mesh network can work as long as their is some power. And i wrote the other day about individual power for each community.

I didn't do the scrip story justice. the actual stories are out there on the net.
There is also wooden nickels.