Backblaze does not support the inclusion of removable media in Backblaze backups, including CD's, DVD'd, SD cards, zip disks, floppy disks, and other similar storage devices.
To backup this data it would need to be moved to an internal drive, or a drive connected via USB, Firewire, or Thunderbolt.
Flash keys may or may not be able to backup depending on it's designation. If it is designated by your operating system as temporary storage which cannot be changed. If this is the case Backblaze will be unable to backup this drive, and you will need to copy these files to another backed up drive to backup the files.