Smoking.

I was around then too, and most, or at least half, of all adults smoked. Most public buildings always had a haze of cigarette smoke in them. So I think Stranger Things is fairly accurate with regards to smoking. A lot of smoking in films is now done with CGI anyway. If you look closely, you'll notice and you'll also see many actors don't take puffs on their cigarettes, they just light them then the camera pans away then they hold them, but you don't see them inhale or exhale.

One thing you don't see much in period dramas is pipe smoking, which was much more common in the old days than it is now. Probably because smoking a pipe takes a bit of practice and it's not something that can be easily picked up by a non-smoker.

I'd say more than half of the adults I knew smoked too. Christmastime when my family got together there was like a cloud of it in the basement where we opened presents.

Only a couple of my family smoke today.