At 8:34 You see Sheldon Stationery a reference to Paul Sheldon from the book, Misery.
When The Kid (Bill Skarsgård) arrives in Castle Rock via taxi, there is a '58 Plymouth Fury in the parking lot. The same car was featured in the novel and movie, Christine (1983), written by Stephen King.
Cans of Moxie can be seen while Henry is listening to the cassette tapes. Moxie is soft drink which originates in New England and is a Maine staple. There is a Moxie Festival every year in Lisbon Falls Maine which celebrates the drink. Lisbon Falls is the home of Jake Epping, the main character from Stephen King's novel 11.22.63.
When The Kid (Bill Skarsgård) walks through the town of Castle Rock after getting out of a taxi, there is a shop in the background called "Claiborne Creamery". This is a reference to the book and movie, Dolores Claiborne (1995), written by Stephen King.
When Henry is dropped off at the Fall Festival you can see a shop named Callahan's Thrifty Lot. This is a reference to the recurring character Father Donald Frank Callahan. He first appeared in the book 'Salem's Lot and went on to appear in the The Dark Tower V, VI and VII books.