External Hard Disk Case - Envelope
Buy an air-cap pillowed envelope (A6), make a small cut for the cable and put your 2.5" harddisk drive with its case into the envelope.
Lost and found
Write your adress on it and so it won't get lost anymore.
It's cheap, shockproof and unique.
04_Put your name and number on it and you might be lucky to get it back in case you loose it