I always come home from the supermarket to find out I still got the deposit ticket from the empty bottles in my pocket. They have thereafter the tendency to stick on the fridge with a magnet for mostly a year and then bleached out to much in the sun. No money for me then.
So this combines a shopping-trolley coin (euro size) and a clip to hold those tickets and your shopping-list. As an extra it will hold a Airmiles card, a customer card from the supermarket where I usually buy groceries.
This design still needs a bit of work because some parts are to thin and I'm not pleased yet with the coin, which has to flip out, is attached to the clip. I will adapt the design later.
I've printed this prototype on a Printrbot LC with a resolution of 0.15 (the clip) and 0.10 (the coin).
I've used 123D Design app for iPad. Although it lacks quite some precision I love to work with it. With some tricks you can get quite some nice results.