There is provided a container having both male and female sealing regions disposed about its periphery in a pattern making it possible to seal a container with another container having substantially identical sealing regions. The male sealing regions used in the practice of the present invention may take the form of a U-shaped ridge which is undercut along at least one leg of the U in a radial direction. Typically, a container will be thermoformed from lightweight thermoplastic material giving the U-shaped ridge considerable flexibility. The female sealing regions used in the practice of the invention may take the form of an undercut channel adapted to receive and match the undercut U-shaped ridges found in the male portion of the container wherein the walls and base of the channel are sufficiently flexible that the undercut portions of the U-shaped ridge are urged into engagement with the undercut portions of the channel. Transition regions between the channels and ridges have arculate undercut profiles to further seal the container. The containers are further provided with asymmetric stacking features and inclined separator tabs.