A list of things that are anywhere from very common to universally accepted in almost every Supercorp fanfic. Most of these are so prevalent in fanfic that I thought they were part of the show until I actually watched it and realized they weren't.
- Lena calling Kara "darling." By far the biggest offender. I really thought people were out for blood for the queerbaiting if writers went so far as to have Lena call Kara darling in canon but nope, never calls her that in the show. (Not that it invalidates the arguments that writers did queerbait.) I have maybe read 2 or 3 fics ever that used any other nickname. How did fanfic writers collectively agree on this? I'm impressed, really.
- Jess being a prominent part of Lena's daily work life. I expected Jess to be present in the show for more than the 10 seconds when Kara barges in for fight club info. Instead, she shows up, makes indignant faces at Kara and Lena, and never shows up again. We don't even know what happened to her. At least she got a name, unlike the assistant who replaced Eve. Meanwhile, any fic that involves Kara and Lena's dates in the middle of the work day, features Jess prominently, sometimes even as a main character. Canon never shows what kind of relationship Lena has with her assistants, yet in fanon Jess is always the considerate, loyal, and mothering ally. Even in fics set in future seasons, Jess always somehow manages to end up working for Lena again.
- Lena's raising one eyebrow. Yes, she does this in the show quite a bit, but she does use arch both brows too. Fanfics emphasize the single eyebrow arch until it becomes silly.
- Listening and homing in on heartbeats. Kara only does this twice in the show, and both times she was singling out on a known source without external noise to distract her. Yet fanon depicts Kara as constantly searching heartbeats, especially Lena's, to check her wellbeing. From miles away, even. And Kara even has heartbeat recognition powers.
- Lena's stealing Kara's NCU hoodie to wear. Did Kara ever wear an NCU hoodie in the show??
- Lena staying in Kara's apartment almost permanently after the Phantom Zone arc. I get it, easy way to play up the emotional attachment.