Interesting holiday .. it was founded in 1938 in part to honor the Salvation Army volunteers who handed out doughnuts to the "Doughboys" of WWI.
Anyway, to celebrate:
Krispy Kreme is giving away a free doughnut of any variety.
Dunkin' Donuts is giving away a doughnut, provided you buy a beverage. (Personally, I hope it can be something other than coffee ....)
If Tim Horton's participates this year, I'll update ...
Also, check with your local shop ... they may be giving away goodies, too.