Hard cases for storing portable 2.5 inch hard drives / SSDs are quite good, such as these ones by Inateck:
https://www.amazon.co.uk/dp/B00L35UID0
(I'm sure very similar cases are available with different brands.)
The main downside is that the cases are about 35 mm thick, although that does mean you can fit two Voyager or DM42 sized calculators inside. (I tried a HP-42S and it didn't quite fit, but a DM42 is a snug fit.)
Case for Voyager 'L' size
Re: Case for Voyager 'L' size
interesting, thanks!
Cambridge, UK
41CL/DM41X 12/15C/16C DM15/16 17B/II/II+ 28S 42S/DM42 32SII 48GX 50g 35s WP34S PrimeG2 WP43S/pilot
Casio, Rockwell 18R
41CL/DM41X 12/15C/16C DM15/16 17B/II/II+ 28S 42S/DM42 32SII 48GX 50g 35s WP34S PrimeG2 WP43S/pilot
Casio, Rockwell 18R