Quote from Random.Capital:
The group that figures out it needs all three to survive.
You should go back and watch The Road Warrior. Tell me what use gold or silver would have been. The valuable commodities will become food, water, fuel, and of course guns and ammo.
In a total collapse of the economy where the dollar becomes as useful as toilet paper, most people are not going to have gold or silver therefore it is going to become completely useless as a currency. Currency is only useful if the majority of the people have at least a small amount and everyone considers it valuable. The new currency would actually become a barter system where only goods that can help in the survival of the people would be considered valuable. Food and water will become top priority for most but anyone without a good strength in numbers and lots of weaponry will find their food and water rapidly stolen by those that have the guns but no food.
