Of all places, Cracked.com has an article on this subject:
"7 Bizarre Things (and 1 Bodily Fluid) People Use As Currency"
http://www.cracked.com/article_16709...ser4=flashback
Of interest is how bottle caps are used as currency in Cameroon, and how Canadian Tire money is used as a currency across Canada and occasionally the northern USA. One town in Columbia uses cocaine as money, and I believe that drugs will also be used for trading due to its value in many areas of North America and Europe. (For that matter I believe that the drug trade will be alive and well for many reasons.)
During the Great Depression some communities issued their own locally-backed scrip, and of course before then individual banks and companies issued scrip, too.
http://en.wikipedia.org/wiki/Scrip
Bottle caps, while silly-seeming, have the advantage of being relatively rare (now) and not that easy to duplicate. A community might come across a store of them (seizing a local collection or stockpile) and issue them as a local scrip backed by some kind of guarantee. In Morrow Project, a team in one game issued a community scrip backed by Project resources (the contents of a local supply base and the team caches).
Tony