I've got it! You can get some of those toy decals or magnets and make it the Magic Pumpkin Sleigh! If you wear a Santa hat as you drive, you're Mrs. Santa dropping off a shipment for good girls and boys. Throw in a wreath around your license plate for good measure or some lights in the window. Spray some of that snow in your windows too. It wouldn't be too much of a stretch considering Nightmare Before Christmas is so popular. I can just see you handing out mini candy canes to folks.
I just thought of this: If not toys, then Christmas items like nutcrackers, angels, ornaments, Christmas trees, Santas, stockings, snowflakes, etc. Your car would look just like a float in the Christmas parade!
~On the 13th day of Christmas, my ghoul love gave to me...~