An acquaintance of mine once made savvy use of available technology to keep a backup of his doctoral thesis: worked fine, until his central heating sprang a leak and soaked the box of punched tape …

I'd be minded to save .txt backups from time to time, as well as fully-formatted .doc/.docx. Thinking as I type, I might try .html as well, to retain an idea of the formatting for the day when I had to reconstruct it <g>

Wandering slightly off-thread, I find I'm doing more and more in structured XML anyway.