What makes something valuable - beyond its actual value as a item - is the belief of the people that its valuable. Hence the term fiat money for nonsubstancial money (latin: fiat = faith, belief).
As long as the people have faith in a currency, it works all nicely, especially for the government and the banks. Everybody accepts that a little piece of paper can buy food, cloth or pay the rent.
But if this faith is damaged, things can turn ugly very quickly. If people start to think that their money has no value anymore - like it easily happens in a inflation - a downward spiral begins. Then a bread or a chicken is much more worth than a box full of bank notes.