I'm trying to find a small case for a couple of pens and a short pencil, but the inner slots keep making the usable space awkward. I don't need every tool held in its own place; one plain compartment that opens wide would be much less faff.
The slots aren't the only space thief. Check the inside width at the narrowest point, since a chunky zip seam can leave two pens sitting awkwardly side by side.
Pen clips eat into that side-by-side space too, and can catch on the lining when you pull a pen out.