Tandem magazines store tray blanks of different size for loading product in different pack patterns. Each magazine has a depending cam device that engages unique lugs on the tray conveyor to allow the lowermost blank to be received on the tray conveyor, and then to be gripped by the unique lug for transport downstream toward the load station. Since only one magazine is used at one time these cam devices can be deactivated as desired. One of the two blank withdrawing means associated with each magazine is located under the tray blank conveyor and operates in timed relationship with it. The blank withdrawing means are also selectively deactivated for the same reason.