The replies here are excellent (as usual!) but they are mostly tactics, not strategy. Establish a strategy first, then select tactics to achieve that strategy. Nailing down the right strategy helps you 1) discover threats you didn't think of and 2) avoid wasting resources on poor tactics. It takes a little more up-front effort but the payoff is worth it.
A good example of a valid strategy (followed by tactics) is
Listening to Katrina. Use it as a starting place, not gospel, then decide on YOUR strategy and follow up with appropriate tactics.
For a strategy start by risk ranking your information, i.e. decide what is most valuable to you.
I have an Accounts folder that gets backed up, it has my spreadsheet where I list each bill and when I paid it on a 12 month grid as well as a budget based on those, then subfolders with statements and documents from each.
Then a personal folder for each person which has their medical records, school records, individual accounts, etc.
Then the pictures, music, etc like most people have. Then an Archive folder, if you change jobs, or close an account then those subfolders move under Archive.
So priority 1 is the accounts and personal, then priority 2 is the pictures, music, archive. Then priority three are things I could recreate such as Reference which are documents downloaded from the internet or the virtual machines I test things on or the general Downloads folder.
Priority 1 stuff gets copied to a pair of drives in USB enclosures,one online on the server the other in the safe, going to add the third back in shortly for the offsite. Those Priority 1 folders also get burned to a DVD and stored with the paper version of them in the important documents binder in the safe as well as offsite. I actually have a bluray burner but since I don't have another bluray reader at my home or my parents home yet I still burn on dvd's.
Another strategy is to ensure data is in as open format as possible, no issues accessing data due to a program not activating or new versions not supporting the old file format after an upgrade. So my spreadsheets are done in OpenDocumet format for example.
My electronic copies are organized the same way as the paper so I could easily make a copy of the whole important documents binder by opening the master document and printing it. Originals are color scanned and linked into the master and the paper version is organized similar with one section for the shared things and one section for each person.
Then I always have more than one laptop, if we buy ourselves a new one the old one becomes the file/backup server. Should we loose one laptop the old is kept up to date so we could just use it to access the backup copy of our data.