I know this is an old thread... but if anyone is still following it...
Boxing Day did originate in the UK and is celebrated on the Feast of St. Stephen, who was the first Christian martyr. The origin of the name is somewhat disputed, whether it was in honor of lords, earls, etc. sending home boxes of supplies to those who lived on their homesteads or sending gifts to the houses of servants who were allowed to visit home on the day after Christmas but not the holiday itself. Its origin has nothing to do with shopping, returning goods, the sport of boxing, etc.