A token to unlock chained up shopping trollies and a keyring clip to keep it in.
Warning: As yet untested and unprinted. The overhang is small but I honestly don't know how it will come out. I'm not even sure if there will be enough flex in the clip to slot in the token. If it doesn't work I will figure out a way of printing the clip in halves and clipping it together.
Update: I managed to print it and the overhang only needed a little bit of cleaning up. The token feels like it would come loose so I will add back more material for the clip. Also the keyring mount is way too small - will fix that shortly too.
Update: I can confirm that the token works with the trollies at my local supermarket. I still haven't gotten round to updating the keyring clip.
Update: I have modified the keyring clip with more material to grip the token and a larger eye for clipping to a keyring. I haven't printed this yet so it may not be right.
My local supermarket put chains on the trollies. I didn't have any change handy and wondered if I could print something the right size. This is the result.
I'm tempted to print a load of tokens with web addresses embedded in them and leave them in the trollies for others to find...
Print out, snap token into keyring clip and go shopping safe in the knowledge that you will never be short of a pound coin sized plastic token ever again.