Take a look at the newest items coming to the Station Marketplace! These items will be available on December 22, 2009.
The backpacks go in a bag slot in your inventory. They take up a cloak appearance slot, so will overwrite whatever cloak you are wearing. In order to set the backpack as your cloak appearance, right click and choose the option to set as appearance after placing it in one of the six bag slots.
To purchase these items in-game, type /marketplace or click on the Marketplace tab in the EQII menu.