> Surely you are not trying to claim that anything which has any value is a viable currency?

Obviously you're not going around trading ramen and cigarettes, but if you live in a some closed system like a prison, then yes, anything of value can be used as a currency. History shows many societies have used many different things as money. Eventually gold out-competed those monies and became the de facto standard for money. You forget that US dollars were originally promissory notes for redeeming gold at a bank; this is what gave US notes value (trust that you could get gold for the notes), and the de-pegging of gold gave birth to the experiment that is modern day banking.