Sometimes it surprises me how many of these I can think of. It's alarming to have "When I was your age, we had [thing] and it sucked" stories and to have told them. I can't be that old...
-Tags on T-shirts. These aren't actually completely gone, I guess, but I haven't owned a T-shirt with a tag for a long time and I am eternally grateful to whoever decided to start printing the shirt info on the inside of the shirt.
-VHS. Rewinding, the amount of space a tape took, the fragility of the things, my god. If all VHS tapes and VCRs vanished suddenly, they would not be missed.
-Disposable cameras. I seem to remember dozens of these things lying around my house when I was little, used up, and never being taken to the 1-hour photo.