Back in World 3 I was in a village that used tin coins as currency. There was a strict rule of "No outside trading" though, so you couldn't just trade for some tin bars and make your own coins. Of course this rule is virtually impossible to enforce. You could really only use coins as currency in a tight, trustworthy group - but if everyone is so loving and trusting you would just share everything anyway.
The system used was basically this:
3 Village claims on the same river system.
There were vending stands in each village and people would just post like 10 coins for 10 raw rabbit meat or something.
IIRC the village had one or two tin mines which were strictly locked down to the leadership so they controlled the minting.
I'm not sure if people took advantage of outside trade or not, I certainly didn't.