I went on a long trip with a mirrorless camera and a SanDisk 500GB portable disk. My "computer-less" backup solution was a Pi-esque machine with USB3 (a RockPi), a powerbank, a card reader, and connecting my phone over USB and tethering it. This gave the RockPi an IP I could ssh into, and I'd ssh from the phone and ran rsync to copy the images from the SD card in the reader to the SanDisk portable drive.
I should make a custom Linux image for the Pi4+ (the whole process is probably too slow without USB3) and some automation (Jenkins?) to do this, I'm sure there's photographers who'd find it useful.
Personally, these days I have less of a need for that kind of thing, given that I can just plug the camera or disk into my phone directly (I suspect a powered USB hub and plugging in both at the same time might even work as well?), but I vaguely recall dedicated "copy everything off this card onto a hard drive" devices being sold, and I don't doubt that some photographers still use these in their workflow.
I should make a custom Linux image for the Pi4+ (the whole process is probably too slow without USB3) and some automation (Jenkins?) to do this, I'm sure there's photographers who'd find it useful.