Backup to USB Flash Drive
Everyone probably knows you should regularly backup your work in case your hard drive fails. It is recommended you back up to a different hard drive or device so if your primary drive fails, you don't loose all your data.
If you don't have a second internal hard drive or an external hard drive, consider using a USB flash drive. They are ultra cheap and very reliable as there are no moving parts.
They will not hold as much as a hard drive, so don't count on backing up your music collection, but you would be surprised how much data (such as resumes and school work) you can fit on a 512 MB drive.