This episode takes place on July 2, 1985.
Lucas (Caleb McLaughlin) wears a cap of an Italian cycling team, Ceramiche Ariostea, from Reggio Emilia, active in professionalism from 1984 to 1993.
Dacre Montgomery was smeared with clear lip gloss to make him look hot and sweaty for the scenes shot in the sauna, as it was never actually turned on during any of the takes.
The two comic books Max (Sadie Sink) offers Eleven (Millie Bobby Brown) are Wonder Woman #326 (cover dated July 1985) and Green Lantern #185 (cover dated February 1985), both published by DC Comics. (Wonder Woman #324, cover dated April 1985, can be seen on Max's bed later in the scene.)
Jordan Lake is in Chapel Hill, North Carolina. That's the state where Matt Duffer and Ross Duffer were born.