That is true. For instance I have a shit load of water and no one can find it, that now become way way more valuable then gold. Where I could trade some water for gold. But I know I wouldn't trade water for any fiat curancy, because if I wanted paper I would ask my printer.
Things like seeds water fule are all good things. But they would be sold for other goods or gold and silver. So if you did find a guy willing to sell some water or food, for a currency it would most likely be some kind of precious metal .