Bad things happen. There's not much you can do to prevent that. Bad things range all the way from catastrophic earthquakes or hurricanes to relatively common problems like a fried motherboard or hard drive. Though you can never prevent those types of things from happening, you can take measures to protect yourself from the resulting damage when it comes to your website.
The web presents interesting challenges with regards to disaster recovery. The virtual nature of the web means that many regional phenomena that will affect you where you live may have no effect on your website. The flipside though is that is that you can be running a website out of Halifax, Nova Scotia, but have an earthquake in California take down your website because that's where your hosting company has its data centers.
When you combine these issues with the fact that digital media tend to be far more fragile when compared to traditional paper documents. I'm sure you can appreciate why we need a different kind of disaster recovery plan than a traditional bricks and mortar operation.
As far as your disaster recovery plan is concerned, your website is composed of three parts. Those three parts are (1) what you need in order for users to view the website (2) the tools you need to maintain the website and (3) the things you need for new development on your website.