I’m confused
It used to be that paper currency was backed by gold and silver for its value. A 10$ paper note would be redeemable for 10$ worth of gold or silver following the gold or silver standard. Currently our bills are fiat money which means they are not backed by any tangible item. They’re just based on the strength of the economy. The economy can fluctuate so it makes the actual value of a bill unstable. These Mcdonalds coins, however, would be a currency that are redeemable for a Big Mac. This would make them a technically more stable currency as they are always have the value of a Big Mac they can be redeemed for.
This is NOT what makes for a stable currency.
One of the problems with specie currency is that it is unstable as hell. Gold rush? Hyper inflation. Ship full of gold sinks? Deflation. No gold is discovered? Lol buddy. I hope your economy doesn’t need to pay for things like food.
The boom/bust cycle happened ALL THE TIME with specie currency. Literally we have records of the Roman Republic dealing with this bullshit.
Fiat currency is the solution to that instability. Fiat currency is based on the “full faith and credit” of the issuing authority. Which means that your money is good as long as your government doesn’t collapse. (if your government collapses, you have other problems)
This is exactly the reason you don’t see any sort of US dime or quarter from before 1964 in circulation, but you can, with patience, find nickles all the back to the first year they were made – the price of silver went up enough that there was more silver in the coins than the face value of the coin, that there were actual shortages of coins because there wasn’t enough silver to mint more, and the government had to change the composition to copper and nickel.
https://en.wikipedia.org/wiki/Coinage_Act_of_1965
(This sort of also happened with the copper in a penny (it was replaced by zinc), but thats less visually obvious)