When Meg is sitting in her room wearing underwear, a baseball catcher's mask, and throwing a ball into her mitt is similar to Tom Cruise in Risky Business (1983).
The non-animated clip is of tennis great Jimmy Connors in the 1991 US Open quarterfinals match versus Paul Haarhuis. Connors, well past his prime at this point in his career, made an improbable run to the semi-finals at age 39, with tremendous support from New York City's often raucous crowds.
A little person dressed as an elf tells Meg she might find Santa at the "Warwick Mall". This could be a reference to actor Warwick Davis, who is a little person.
The flyer advertising the winter concert reads "we can't say Christmas because of that one family" this is likely a reference to the Goldmans who are Jewish.