Abstract: A flat-storable container comprises a bottom deck and a pair of opposed sidewalls attached to the bottom deck in hinged relation thereto, to permit the sidewalls to lie flat against the deck in a folded position, and to stand in perpendicular relation thereto in a container-forming position. The sidewalls each typically carry a pair of opposed, foldable side flaps which are proportioned to be unfolded in the container-forming position to form lateral walls between the sidewalls. Thus, sets of the engaging side flaps define lateral container walls extending between ends of the opposed sidewalls, to define with the deck an open-top, rectangular container. A container lid is typically provided, plus straps for holding the lid on the container and for holding engaging side flaps together, when engaging side flaps are used. Alternatively each lateral wall may be defined by a single side flap. Such containers may be of relatively large size, and used in airliner baggage compartments or any other desired use.