Overview:

I designed these bit holders within the Gridfinity system by Zach Freedman.  The 2x2 version holds five standard small plastic bit cases, and the 2x4 holds five small and five medium cases.  Both versions are stackable.

I also designed cases and plugs for bits that did not come with a case: https://www.nexprint.com/en/models/G7191662

Printing:

These can be printed in any filament.  No supports required if printed in the orientation shown.