It is very needed to be able to create a packaging slip per box. Like once it is settled that a shipment has X number of boxes it could appear a dropdown beside each item to select which box they are in.
Or the possibility of printing a packaging slip with only selected items within a shipment. So when printing a packaging slip a prompt window appears asking if you want to do a packaging slip for all the items or partial items, and when clicking partial they allow you to select the items and quantity similar dynamic that is already there when splitting the shipment.