My socket extensions were rolling around my toolbox so I designed a tray to hold them all.

I designed the tray to hold the following:

(3) 1/2-inch drive (3, 5, 10 inches)
(3) 3/8-inch drive (3, 6, 10 inches)
(3) 1/4-inch drive (2, 4, 6 inches)
(1) 1/2-inch drive to 3/8-inch drive reducer

I had to cut it in half in order to print it and each half is held together with 4 magnets (3mmx9mm)