I use a external HD to back up My Docs, pictures, music all that stuff. Programs can be replaced, personal stuff not so much. I actually just started exporting my emails for backup too. I can't believe it took me so long to do that.

I also started backing up my online Bookmarks.

I have copies of my passport, DL, CC's and contact numbers on a thumb drive in case I lose any of that.

Its also good to back up your cell phone using your sim card or some of the new phones can be downloaded at the store.