Here's Star Wars Darth Vader Back Buddy, which Entertainment Earth touts:
Have the power of the Dark Side on your back at all times! The back pack features Darth Vader's helmet as he clings to your back. This item makes a great gift for those still in school, or for Star Wars convention-goers with just too many things to carry on their hands!
It's a good thing your kid has the power of the Dark Side, if not he'll probably get beat up in school... Link - via GeekAlerts