I use old soft plastic boxes in which GW used to stuff their boxed metal miniatures, all set into IKEA jewellery drawers.

These are great because they're very small, stackable, easy to label and compartimentalise, and on top of that, they're way nicer than the bolts-and-nails portable cases. You can even paint them with Old-Worldy motifs, griffins, twin-tailed comets and Gothic fraktur inscriptions saying "Karl Franz Rex", or give it a nice Imperium flavour with some bits and pieces. Fun times!

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I have tens of small zipper bags, and I store them in these moppe drawers. I've got one for 40k stuff, one for WHFB, another one for works in progress (for when I need specific bits handily organised in projects instead of thematics), and a couple more to store the miniatures (I don't have much room for a glass cabin)

I tried it myself with some wood stain satin, metal decorative handles (turn the drawers around so you won't see the small hole-handle) and some tin bends, nicely nailed down. Now all I need is a two-headed eagle shape to stick it at the front and, all set.