In this job, I get to try out a lot of cases, and they're usually plastic, metal, rubber, or fabric. But the Q Card Case for CM4 is an interesting hybrid, combining a soft leather-like fabric where it counts and rubber for the phone case component. They have even applied for a patent for this combination.
The fabric portion has a slot that can hold up to three credit card or ID cards as well as some cash. There's a nice slot that makes it easy to eject the cards as needed.