Steve Perry, former lead vocalist for Journey, has said that the Stranger Things season 4 remix of Journey's 1980s smash hit Separate Ways (Worlds Apart) was done pretty much the way he originally wanted it done in the 1980s, but lacked the technology. Perry was so impressed that he even helped with the development of the remix.
Costume Designer Malgosia Turzanska was searching for a vintage army belt for Lucas in season 1. At an antique store in Utah she found one locked in a cabinet. Upon retrieving the belt she discovered on the back side written in Sharpie: "Lucas", the name of the original owner.
Max's theme song in season 4 is "Running up that Hill" by Kate Bush. The frequent use of the song led to it going to #1 on the US iTunes chart in the first week of the season's release. In 1985, the song did not go higher than #30 on the US Billboard chart.
In a 2016 interview on NPR, the Duffer brothers (Matt Duffer and Ross Duffer) praised the then eleven-year-old Millie Bobby Brown as a precociously gifted actor and said that she is able to adjust her performance to different lens or camera positions in a way that most child actors don't know how to do. But they also said that there were times on the set when they were reminded that she was just a little girl; the example that Ross Duffer gave was, "one day she showed up on set and she [was] just covered head to toe in glitter. And she's like, 'I don't know where this glitter came from.' And it's like "I'm not having this problem with any of my adult actors. David Harbour is not coming in covered in glitter." The Duffers said that removing the glitter delayed their shooting schedule by 45 minutes.