The trouble of a silver standard or a gold standard, even with a fractional reserve system, is that if something that happens in the outside world unpredictably changes the value of silver or gold, you will suddenly change the value of all long term contracts. (...) So the ideal system from my standpoint uses what refers to as commodity bundle. That when my bank goes into the existence, we say - you bring in a million Friedman dollars, we will give you a ton of graded steel plus five hundred bushels of grade B wheat plus two ounces of gold plus... You would have some list of commodities and the bundles what you would redeem. (...) And now since it's very unlikely that all of those different commodities will change their value at the same time, you have something which is more stable, which gives you more consistent, predictable value for the money than any single commodity.

David Friedman