A big chunk of space would take some work, but if you only needed a few KB there is slack space (at least a handful of sectors) on the end of every USB drive th

A big chunk of space would take some work, but if you only needed a few KB there is slack space (at least a handful of sectors) on the end of every USB drive that doesn't align with partition sizes. I've used it before to store data on how many times my reformatting tool was used on the disk.