I found a tray meant for sugar packets is the perfect size for CF cards.
I use the plastic cases as spacers. After I come back from a session and copy the contents to the computer, the CF card goes to the back, behind the marker. I know everything in front of the marker exists in at least two other places (My internal drive and the external backup drive), and are ok to reformat and reuse. When the marker gets close to the front, I need to backup my photos again.