What ought to be backed up?

Everything.

You think not?

OK. Try this test: Right now, delete any folder on your hard drive. Empty your recycle bin.
Do you miss the folder?

Yes: Good thing you have a backup, isn’t it.

No: OK. So that was a useless folder anyway. Repeat the test.


Did you lie to me about deleting the folder?

Yes: Then I’ve called your bluff. Your current backup and recovery system isn’t good enough, is it? You don’t have confidence in it, do you?

Useful Link

Here's a link to a blog article about backing up blog templates. OK, so you don't have a blog. That is not the point.

The point is that even with your hard drive(s) backed up, there are online and offline data sources under your responsibility.