For my "Stanley Tool Organizer System" (Amazon Link) I made some separators with drawers for one of the side panels. There's a lot of space in there, but I rather use this toolbox for storing my carcassonne-tiles and meeples rather than for tools actually, because they just fit perfectly in there.
For my usecase it's a waste of space to leave the side as is, so here's my solution:
unfortunately the few upright walls are not that straight and stiff, but rather wobbly, so the drawers may not fit perfectly, but it works good enought for me.
In case the separators dont fit with your printer (they should have a tight fit) i also added the scad file. it's a bit ugly ant not fully parametric, but it works for smaller adjustments.
have fun and leave me a comment.