There's a day (actually, two) reserved for swapping out the batteries in your smoke detector.
Perhaps today could be a day for backing up all the data you care about. All your music, say, or your passwords or your files.
If you need a hard drive, here are three. (Or be double safe and use Dropbox.) But that's not the hard part. The hard part is doing it before you go to bed tonight. And storing it at a friend's house when you're done.
If you care about it, back it up. (After I wrote this, saw this well done pre-steal).