Hopper (David Harbour) reads Eleven (Millie Bobby Brown) Lucy Maud Montgomery's Anne of Green Gables; he also is shown reading this to his daughter Sarah in Chapter Eight: The Upside Down (2016).
Bob (Sean Astin) gives a pep talk to Will (Noah Schnapp) and tells him about a scary clown 'Baldo' who offered him a balloon at a fair and would scare him every night when he was a kid. This is a reference to Stephen King's novel and movie, IT adapted into It (2017) It (2017) and it's sequel It Chapter Two (2019), and Pennywise, the clown. Also he mentions he grew up in the city of Maine where the story of IT took place, indicating that he had an encounter with Pennywise.
Along with the many other references to the Alien franchise, Dustin's (Gaten Matarazzo) cat, Mews, looks exactly like Ripley's (Sigourney Weaver) cat, Jonesy. Even featuring a shot of it hissing in the presence of danger.
On Google Assistant, there is a game where you talk to Dustin (Gaten Matarazzo) and it's based on this episode. The only change between the game and this episode is that in the episode, Dustin doesn't talk to a stranger on his walkie, while in the game he does, with the stranger of course being the person playing the game.
The costume Dustin's mom is wearing at the beginning of the episode is a reference to E. T. It appears to be based on the costume Elliot's mom is wearing when she sends the kids out for trick or treating.