To me when it comes cultural Christianity I rate Christmas Carols number 1. They are available to almost everyone, are beautiful, moving, and imbued through and through with the message. The tunes and words almost everyone knows and singing them is wonderful. My favorite is O Little Town of Bethlehem but almost all of them are timeless and thus they pass the true test of art.
It always made sense that the TV ads first began appearing every year before Halloween. This was back in the day before online shopping and overnight deliveries, and at the end of the ad the announcer always said: "Allow four to six weeks for delivery." LOL.