Not all data backup methods are created equal. Depending on how critical your files are, you need to consider which method is most appropriate.
Separate physical hard drive: Fast, cheap storage. Readily available. Can be networked from another computer or connected to wirelessly when connected to a wireless modem.
Optical recordable media: Cheap, readily available.
Flash drive or USB drive: Inexpensive, easily portable, fairly fast, reusable.
Third Party Network Storage Space (Free): Can be accessed over the Web via any computer and often any portable smart device.
NCSU Drive / AFS Space: Maintained by NC State; backed up, secure, local support.
Google Drive / Docs: Free, constant saving while you work.