A backpack used to carry beer, wine, liquor, or anything illegal to and from house parties, clubs, or frats. Usually used to hide alcoholic beverages from cops, as well as a way to transport alcohol from one place to another when walking.
"Yo Kevin, heard they are charging 5 bucks for a cup at 409, pack the beer in the booze backpack we'll bring our own."
"The cops might be out tonite will take the booze backpack through campus."