I've an encrypted backup disk from 2009 with personal files, including an unknown quantity of bitcoin on it. Bitcoin was rather easily mined back then and I was working as a sysadmin with pretty powerful servers sitting idle. I lost interest because bitcoin wasn't worth anything and I couldn't use them, so I moved on, moved countries, stored the disk in my mums attic and forgot about it.
Unfortunately I've long forgotten the key and I'm just keeping it in case I remember it in a dream or something... Lol