Make or buy Christmas cards and spend the evening addressing the envelopes and adding a message to each card. Send out hundreds or just a handful.
Set up an assembly line, if you like, with one person addressing the envelopes, one person stuffing them, somebody licking the flap and someone else adding a stamp. If you're feeling crafty, the post office sells special Christmas stamps for that finishing touch.
Make sure your mugs are full of hot chocolate, mint tea, eggnog or hot cider to keep you well-fortified for this task!