Containers of the wraparound and tray style are provided, having enhanced stacking strength and general robustness, through the provision of internal and external reinforcing panels and flanges. Variations of the basic invention are provided with closure flaps of varying configuration and placement; end walls and minor flaps with angled side edges to provide for containers having inclined sides; regions of weakness, removable portions of panels and/or preformed apertures to permit conversion of the containers to display/merchandising modes; gusseted corner structures to provide for containment of fluent materials; and enhanced transverse support structures.