The meta answer is
SLEIGH.
OK, the inspiration for this one was obviously the time of year. I also wanted to experiment with a hide-words-in-wacky-themers type of puzzle. So, sharp- (or probably even blunt-) eyed solvers noticed that there were six rather unusual entries:
17A Standard way a famous king might answer the phone = MIDASHERE
21A Legal doc. verifying a type of car's roadworthiness, say = SEDANCERT
26A "Everyone wants internet origin stories from me, because my ____" = POPRANCERN [the web started at CERN]
48A Italian fountain's noble gas? = TREVIXENON
53A Greater environs of a central Texas populated area = WACOMETRO
64A Hero of an English football tournament, perhaps = FACUPIDOL
With a prompt from the title to think Christmas thoughts, it doesn't take too long to spot one of Santa's famous reindeer hiding in each of these themers (as shown below). So what is a mode of transport associated with these reindeer? Why, Santa's SLEIGH of course, so SLEIGH is our meta answer. Not a difficult leap, but also not a required one, because if we examine the first letters of the theme clues, low and behold, they explicitly spell out the answer.
But wait you say, what about poor DONNER and BLITZEN? Well, turns out there was no room for them in the grid (it was hard enough to fill as-is
). But they're not totally left out: as shown below they're hiding in the clues for 16A and 66A, respectively. Plus, the last two reindeer were originally DUNDER and BLIXEM apparently, so for good measure they can be found in the 9A and 69A clues.
Finally, thanks to
@Wendy Walker for asking after RUDOLPH, who wasn't initially included. And for co-constructing the new 19A clue that fixed that problem.
Hope everyone enjoyed, and thanks as always for the kind comments.