The backpack has a main body that unfolds to lie flat providing ready access to the contents of the pack and various separate accessory pouches carried within the main body of the pack. The main body of the backpack is formed by a flat back panel, a pair of flat side panels and a top panel. The side panels and the top panel are integrally connected to the back panel and fold together to fashion the main body of the backpack in a folded orientation and unfold to lie flat side-by-side in an unfolded orientation. The panels are adapted to selectively support a variety of detachable accessory pouches. They provide compartment for stowing items to be carried in the backpack.