From what I've read, a ‘Christmas Box’ in Britain is a name for a Christmas present, and Boxing Day was a day off for servants when they received a ‘Christmas Box’ from the master. The servants would also go home to give ‘Christmas Boxes’ to their families. Boxing Day is also a time spent with family or friends, usually those not seen on Christmas Day itself.
Personally, anything that prolongs gift giving is good as far as I'm concerned!
