I only have three files that are of such importaince that it merits "special treatment": My digital signature (in denmark, you can pay your phone bills and report your taxes with these) and a key pair for my internet banking logon.
What do I do with them? I keep backups on almost any data carying device within my grasp; laptop, server, mp3 player.
I don't explicitely encrypt these files, because they are inherently secure by them selves, meaning that you need to know the password before you can make use of them - and the passwords I use for these files are strong (rainbow crack is highly unlikely and John is not in your lifetime).
