Stock Day
Here in Canada, Boxing Day is something like the U.S. Black Friday - a day (or a week) to brave insanely crowded stores for a few sales. That said, I think a better use of Boxing Day, if you're fortunate enough to have it off, is to stay home and make stock. All it takes is a pot, the bones and whatnot from Christmas dinner, and some veg. You put your feet up and relax, maybe skim the pot now and then. Warm up the house and enjoy the smell of something good on the stove.
Maybe you don't have a ton of swag at the end of the day, but after the excess of Christmas, there's a certain satisfaction in making the most of what you've got.