1)Haul things in a backpack
2)Accost Jay Leno with a backpack.
3)Fill backpack with bananas and leave in the middle of a large intersection while filming from the book depository with an awesome sniper-camera for YouTube upload.
4)Put backpack in larger backpack to transport backpack...but that would require two backpacks.
5)Understand Quantum Mechanics while wearing a backpack.
6)Contemplate the reason for such a site to settle on the number 'six' for such a question...while a computer is being held level only with support of a backpack.