1. Nancy Wheeler discovers there's something wrong in Hawkins before any of the other characters.
Nancy works at The Hawkins Post in season 3, mostly getting the employees their lunches and coffees, and generally being treated like shit. Despite this however, her conviction that something is seriously wrong in their town makes her stand up to the bullies and chase the story.
2. Joyce's theory about why her fridge magnets fell off leads to the uncovering of a massive conspiracy.
Joyce might come off as pretty eccentric, but most of the time her gut instinct pays off. So when the magnets on her fridge get demagnetised, she goes looking for answers. The school science teacher helps her out, and suddenly she's back on the trail looking for answers.
3. Robin freakin' cracks a top secret Russian code.
Dustin picks up a strange feed on his amped-up ham radio, but he and Steve have absolutely no luck figuring it out. Enter Robin, who's ears are like 'little geniuses'. She works diligently, figuring out the sounds of Russian letters before putting them together and creating a legible sentence.
4. Erica helps the 'scoop troop' gain access to the secret Russian lair.
As annoying as she is, Erica was totally indispensable in this season. She's the only one who can fit into the air ducts in order to open the secret room doors from the inside.
5. Max shows Eleven how to be her own person.
Up until now, Eleven didn't really have an identity of her own. First she was a guinea pig at Hawkins lab, then she was under the protection of Hopper and his rules, followed by spending every second with Mike.
Strong, smart, passionate, and realistic - what a great depiction of women on a show!