It is desirable to have a currency based on usefulness.
In the local Colchester newspaper I read about a man who was given a counterfeit £20 note (about $30) from a banking cash machine. The bank at first refused to pay out, thus the man faced a personal loss of £20, a big loss to some people. Rightly, the bank made a goodwill gesture to recompense their customer for their loss, rather than have a damaging story to their brand of being a cause of loss to customers by giving out forged bank notes.
The above story is the latest of many stories that highlight how worthless base metal and paper currency is. For many people currency has been further reduced to plastic cards and numbers on a computer database. The current system allows for fraud and error to wipe out a life time of an individuals work overnight. Banks and Governments further corrupt currency by their regulations and clever tricks of printing and devaluing money.
Always the value of work of the man that ploughed your field will hold greater value to you than a blank piece of paper. The difference with our current system is that the blank piece of paper is printed with images, and it has a vague subjective promise that you will get something of value for the paper.
The ancient Celts used tangible assets to trade with, for instance cattle. A cow is useful as it can provide meat, milk, transport goods, and pull a plough. The cow only needs grass and water to run itself. The number of cattle owned was a sign of wealth in Celtic society.
The Celts also traded in bronze or gold ingots, coins and axeheads, all that could be converted into beautiful jewellery or useful tools.