Stranger Things might be known for its Easter eggs designed for children of the 1980s, but the most interesting, significant and impactful one of the second season has nothing to do with nostalgia, but rather its own story.
All Stills: Netflix
Throughout the first and second seasons of Stranger Things, we see Chief Hopper donning a blue bracelet. People on Reddit took notice, and actor David Harbour hinted on Twitter that its inclusion was related to his flashback in the final episode of season one.
Turns out, it was the ponytail elastic that his daughter was wearing during the first moment we see them together, playing in the park until she starts wheezing and she has to be taken to the hospital. In the next scene, she's lost her hair from chemotherapy, and Hopper is wearing the hair tie on his wrist as he's comforting her. That hair tie looks to have stayed on his wrist from that moment on.
You can see the hair tie on Hopper's right wrist as he creates the traps for the house.
Hopper and Eleven's relationship was one of the most poignant parts of the second season. Over the course of several months, we see them become a family - for better and worse. Hopper keeps trying to protect Eleven, partially because he feels he failed to protect his own daughter, while Eleven struggles to grow into her own person. After a tense separation and heartfelt reunion, we see their growing bond come to fruition. In the Stranger Things 2 finale, Dr Owens gives Hopper a fake birth certificate declaring "Jane Hopper" his legal daughter.
Later on, when Eleven is at the dance with Mike... she's wearing the blue bracelet.
This might not be as big a standout as the Ghostbusters costumes, the Dungeons and Dragons references, or the retro soundtrack, but it's actually one of the best references Stranger Things has done so far - because it didn't depend on our nostalgia, it was entirely based on the strength of the series and its characters. I'm looking forward to seeing more moments like this in the future.