Get a large USB flash and create an Automator script that goes and gets all the files and folders you want backed up (i.e. Documents, Address Book database, Mail folder...). Additionally, tell it to zip those files, and auto save it to the drive as whatever name you want. When you save this aforementioned as a plugin, just insert your USB into your computer, right click on the desktop and select the automator script from the contextual menu. Sit back and watch it go....