This article from the Guardian illustrates nicely the difference between what we want– goods (“wealth” in terms of political economy) and services– vs. money. Money is a medium of exchange, which we can use to obtain wealth and services, but in itself it really isn’t capable of satisfying our desires. The particular example here is from the town of Volos, whose railway station is pictured.
I could imagine Greece not formally dropping the Euro, but just kind of abandoning it, using local currencies, perhaps eventually united into a new Drachma. It’s not clear from the article whether their government is attempting to tax the alternative-currency transactions. The wiser course would be to tax economic rents instead of transactions, and that could be done in whichever currency is most practical.