For me, pogs were all the rage when I was a kid. It was a game played with circular disks made of thick cardstock (pogs) and metal disk (slammers)

The pogs had different designs. Some were cooler, more desirable. Most kids played the game for keeps but some kids traded them amongst each other. In a way, they were like money "I'll give you 10 pogs if you do my homework" or "I'll trade you 50 pogs for that slammer" and so on.

The fad was crazy but here's where it came apart for my friends and me. A family friend who ran a printing company was hired to print and cut pogs. We visited one day and he handed me a stack of overprints. Each page had about 40 pogs. I was a pog mogul overnight. He literally printed "money" and I had way too many for it to have value anymore.

I think kids naturally gravitate to creating money systems among themselves. They see the world transacting in dollars and instinctively know that money is a way to transfer value. But as a kid, you didn't really have access to "adult money" so you'd make up your own among your peers. I'm interested to see if there are other similar stories out there.