How about purple dittos? They would come from the machine, still wet with alcohol.
And I cringe when I think about the number of times I wrote out a whole worksheet or test, only to realize I had forgotten to remove the tissue paper separating all my hard work from the carbon paper!
And if you made a mistake, you had to very carefully cut off the carbon with a razor blade.
For the record, though, we still have chalkboards. They come in very handy when:
a) you need more than one screen-- I can put a diagram on the board below the screen, or to the side.
b) the wifi (or even the power in general) is being finicky. We lost power for an hour or so earlier this year... I forget why. I found a piece of chalk, opened the blinds for light, and finished my lesson.