A secure container system comprising a first container with a second container mounted thereon, the container having adjacent sides that are complementary to one another. The first container includes a pair of spaced channels and the second channel includes opposite flanges which engage the channels for mounting the second container on the first. The first container has a door which, when closed, includes an extended portion comprising a stop for selectively preventing lateral movement of the second container relative to the first. When the door is opened, the second container may be laterally removed from its mounting on the first container.