Do you mean what we would we do if we found a USB just lying around somewhere? Or do you mean what would we do if had some spare USBs that we like bought and knew were trustworthy?
If it’s the former you leave that thing where you found it, or at least I would.
If it’s the latter, maybe I would play with writing a live boot OS like Tails. Otherwise I use cloud storage to take care of anything I would need a USB for. Used to carry one around with me, but not anymore.