Anyone ever consider this for currency?
Supply and demand. These (and any other medium of exchange) only have value if both parties agree on the value. What you pay for them now may be far more (or less, though unlikely) than their worth in a SHTF scenario.
Think of it this way - You have goods to trade, and someone offers you these in return. How sure are you that the next person you trade with will accept them?
A universal need will always be the best currency.