Simple double ended trolley token in three denominations £ coin US quarter Dollar and One Euro.I have only checked the £ version , the others sized from Dimensions on the internet.The pound one works fine tried at Tesco, M&S local garden centre. The others I haven't tried for the obvious reason.
I thought the double ended idea would give a sensible grip area and as it was plastic actually double the life of the token as you can use it both ways. I never put a key ring hole in it as I didn't think it would be such a good Idea to have your keys hanging on the trolley, better to keep it in your pocket or purse.
More Things to make including 2 working clocks at http://www.3dprinterclocks.com