… that you backup regularly and bring over to any new hard disk/computer.
i still have the savegame for Darklands.
The most useless thing on my hard disk is Microsoft Windows. But I don’t back it up or move it onto new computers. Does that count?
I always put off doing backups
So, I have nothing saved.
That is useless 
Well, I’ve got quite a bit of porn that I never plan to go back to watching, it’s gotta be new, new new!
I’ve also got the config files from an old user profile for a old roommate who hardly ever used my computer and who never saved anything to it after setting up a password.
Save games from Might & Magic 3, 4, and 5.
A BIOS flash from two years ago.
ICQ logs from 1995-2000. I don’t use ICQ anymore.