I usually keep a portion of my Star Cars collection on the mantle. Sometimes however, they need to come down. That sometimes most usually come along around Christmas. My wife prefers to have holiday decorations up on the mantle for a couple months. Usually the cars just get put in a box where they can slide around. This year I cut a piece of polystyrene foam with slots for each vehicle.

I placed the cars where I wanted them with a pen. Then I used a retractable knife set to the depth a wanted to cut along the outline. The foam was built by stacking thinner sheets and gluing them together to make the final thickness. It happens that there is a seam at the depth where I wanted to be. I pulled the piece I wanted to remove and it generally separated nicely.