IOU One Cent
Patriotic Civil War Tokens
This was emergency currency and not an official US Mint denomination. The token allowed trade to continue without official money by claiming the individual presenting it would redeem it with real money once the system was back up and running. Unfortunately, it turned out that when pressed, no one would redeem the tokens requiring the US Government to issue a law making the emergency currency illegal. Too bad there were only about 25 million of these in circulation.