"Let no old yet still functional technology go to waste" is the motto of any good McGyver-class geek, which is what makes the idea of using an abandoned but still capable iPod classic as an emergency boot drive for the Mac so appealing. Chris Breen of Macworld:
The gist is that a bootable iPod can be a very helpful tool when your Mac is refusing to start up or is generally misbehaving, and you'd like to boot it from another drive and use troubleshooting tools on the iPod to diagnose (and, you hope, repair) your Mac.
Again, it's not for the faint-of-nerd, and you will also have to wrestle an OS X installer out of Mountain Lion to complete the job, but when you're done you'll have a potentially very big lifesaver in a very small package.
Check out Breen's article for complete instructions, and if you decide to give it a try, let me know!