This is a low profile modular USB holder which can be customized and attached depending on the USB drive size and number of drives desired.  I had trouble finding one that worked well to stash in a drawer, so I designed one in TinkerCAD.  They interlock and can be glued together, with end-caps which make it into a well contained box.  

The USB connector slots have little ridges to grip the drives, but they are very sensitive to print settings.  You may want to print one of the medium ones first to test the print settings; also supports help under the tiny lip for when they interlock.