"Buddy, you're more of an elf than anyone I've ever met." Coming from Santa, that's high praise indeed, and Ed Asner's warm delivery completely sells it.
Walter apologizing to Buddy for what he said to him at the office (basically I Have No Son).
Emily being immediately accepting of Buddy despite the fact that he's her husband's illegitimate child and seems kind of insane.
When Jovie starts to sing "Santa Claus is Comin' to Town", to have everyone join in to generate the necessary Christmas Spirit/Belief in Santa Claus which powers Santa's sleigh's ability to fly.
Buddy meets a young girl named Carolyn in the doctor's office and asks what she wants for Christmas. She responds "a Susie-Talks-A-Lot." And later, as Michael shows Santa's Christmas list on TV, he mentions Carolyn and that exact gift.