I need 7 different cartridges for the computers in my room. When I change one I put the empty box in my school bag as a reminder of which one to buy. It saves time to go to the store and simply ask an employee for the same kind. Also, the color and pix on the box make it simpler than writing a note. After replacing, I keep the empty boxes in a special bag marked for re-ordering and at the end of the school year I have a count of how many of each I needed that year. This method can be used for other supplies that need to be ordered in the spring.