A two bin Kanban system is a popular Kanban (a signalling system). In principle it provides a mechanism for stock re-ordering.
Starting out with two full boxes when one of the boxes becomes empty it acts as a re-order signal, the second box represents enough material to be consumed while the empty box is restocked (bear in mind this could be carried out from an internal warehouse or 3rd party supplier). Commonly a Kanban card may accompany the box which carries certain information about the inventory required.
Kanban systems are quite common in industry – for an example of Kanban in operation click here
