Since Rekordbox5 RB has the ability to import everything back from a CDJ prepared USB. This functionality is not without flaws (the import sometimes forgets the cues/loops which means running it again with the update option)
You'll have to do some trickery to make sure the track files are imported to your external drive (instead of the home folder on your startup drive) but it's doable.
You can see me use it here for an entirely different purpose and you'll also see the error (no cues/loops imported I was talking about and how to correct it)
If your external drive is HFS (+) formatted it's word to check out the hidden Pioneer folder to see if the database is located there (with some relevant backups).