I predominately use 3 grits of sandpaper with my orbital sander. 80, something else, and something else. I was tired of them sitting on a table only to fall off, or trying to use the packaging as some kind of clever tray when it wasn't.
I decided to make a caddy, which I could hang on my storage wall with a French cleat.
Step 1: Plywood and Then Some Holes
Draw a center line lengthwise. Use that to line up your discs and trace three holes each. You could go more, but I see no reason. Three looks like a face and who doesn't like that?
3/8" dowel rod fits the holes prefectly, therefore I drilled my holes with a 3/8" forstner bit. I went 1/2" deep, but you can do whatever you want.