Not technically a single file on disk anymore, but I still have an old text file of software registration keys / serial numbers that I started in the 90s, for b

Not technically a single file on disk anymore, but I still have an old text file of software registration keys / serial numbers that I started in the 90s, for buying shareware or ripping CD keys with Magical Jellybean (a Microsoft key ripper). It started life as a plain .txt on disk that I'd manually copy over from computer to computer, first via floppies and eventually null modem cables and ZIP disks and thumb drives. When email got popular I started emailing it to myself as a way of storing it in the cloud. Eventually it made it into Gmail and I could store it there, versioned, across generations of computer platforms and ISPs. Then Google Docs came around and it's lived there ever since. I still go through the version history there sometimes. It doesn't go all the way back, but does have some interim license keys if I ever need an older version (like some gray market version of Windows 7 for a refurb laptop).