In my world (like in Fallout) the “money” it hasn’t value anymore, for this reason, the Merchants created a new currency: the Tokens. The reason behind this is that after the GWFCE attack, a lot of survivors take shelter in the Trade Cities that were full of supplies. When space has begun to be little, the residents started to close the doors and ask for goodies or supplies in exchange to pass a night in a safe place or to get some stuff. To put a price to the supplies, the survivors started to use the Tokens from the Trade Cities (similar to the casino tokens) and put it in boards like this:
Water = 100 Tokens
Canned Food = 50 Tokens
Blankets and Winter Clothing = 10 Tokens
This way the visitors could know the actual prices and the necessities of each Trade City. The survivors also started to “pay” the visitors whit this currency to allow them spent it inside of the Cities. Was a controlled trade. With the time the Tokens become in something more important than the supplies and the people started to exchange it for other things outside the Trade Cities, becoming in a little time in the new currency.
The survivors use also the trade to some business.