Brady is listening to the song Pet Sematary by the Ramones. Stephen King, who wrote the novel Mr. Mercedes, also wrote the novel Pet Sematary.
When Deborah asks Brady to join her on the couch, and he refuses, she says 'all work and no play'. 'All work and no play makes Jack a dull boy', is a famous line from The Shining, another novel from Stephen King.
When Bill Hodges initially comes outside to throw the ball back and to shout at the kids, they ask him if he wants to be the goalie in their hockey game and wear the 'jason mask', this is a reference to the Friday the 13th movie series.
This is the second such casting switch for Mr. Mercedes, with the late Anton Yelchin (a.k.a. Pavel Chekov from Star Trek 2009) attached to play Brady Hartsfield. Harry Treadaway (a.k.a. Dr. Victor Frankenstein from TV series Penny Dreadful) signed on in October 2017.