I ran into some students on Friday after class who had gone to Home Depot in search of masonite panels and were told that they didn't carry them. I did some detective work later that day and found that they indeed do have these panels; they apparently just don't realize they do. The official Home Depot name for the panels is:
Tempered Hard Board (get 1/8" or 3/16" thickness)
You can get them in 4x8 ft or 2x4 ft sheets. Remember, cut them into roughly 9x12" panels. You only need 2 for Monday, but you might as well prepare a dozen or so. This should last the entire semester.