Teletext: the forerunner to the internet. There was "Backchat", where teenagers could send in comments, by phone, post, fax; and the excitement when you could do it by email (not many people had it at home then). I remember one comment from about 1997, which I think sums up the whole of modern social media:
"I really love Backchat, because the stupid things you all talk about amuse me. Keep up the good work, everybody, it's so funny!" Now you can just replace the word "Backchat" with "AIBU".
I remember someone in about 2008 wearing a T-shirt saying "Myspace is for losers". If anyone remembers Myspace now (a forerunner to Facebook).
Advertising in shop windows, and in Loot. I miss being able to do that. Now you have to use social media to get any success advertising anything, and you have to make it look pristine with lots of photos, video samples, and so on. I found this out to my cost when I wanted to advertise a local event. Before, I would have just put up a flyer in a few shop windows. Now... where do we begin?