Don't know what Boxing Day is? In the "old" days when the milk man, the butcher, the green grocer, the tin smith (to repair pots and pans), and others used to come to the door, boxing day was the day they each had a little box that the household was to put coins or a gift into as a yearly "treat".
We liked it even in modern days because Christmas could be for family and Boxing day for visiting and cleaning up.