Based on The Alchemist's money clip. I created this two-sided version so I could hold cash one one side and receipts on the other. Could possibly use the second side to hold a debit card, etc.

This clip uses detents to help improve grip. But it still doesn't hold one piece of paper very well. So I used hot air to heat up the joint, and held the clip closed while it cooled. That improved the grip, but made clipping a little more difficult.