I read recently that it's a good idea to have at least three copies of your work. Some suggestions were the hard drive, CD, Zip or Jazz drive, flash drive and hard copy.

If you wanted to have multiple methods, you could get mini CD-RW's (if the 128Mb will hold what you need backed up) and then you could use the same mini RW to back up things time and again, and they are a lot smaller to carry than standard CDs.