Origin of "Cookie" in Computing?
According to the Wikipedia article on magic cookie, it was used already in 1979 in the manpage of fseek. The talk page of the Wikipedia article on magic cookie discusses questions regarding the origin and meaning of the word. The following quote of Douglas W. Jones from the talk page nicely summarizes it:

Once upon a time, I asked Dennis Ritchie about the origin of the term magic cookie as used in the man page for ftell and fseek in the C library. He said that, so far as he knew, the usage in that man page was a new coinage. That man page is not present in V5 UNIX but it is present in the manuals for V7 UNIX and 4.2BSD. I have quoted the relevant sentence from that manual on the Wikipedia page; the wording makes it clear that the meaning is the same as the contemporary meaning for magic cookie (in the broader sense than HTML cookie). Any speculation about derivation from cookie monsters or LSD cookies seems, at this point, irrelevant compared to tracking down the first use of the term in its modern sense. Douglas W. Jones 21:15, 24 February 2017 (UTC)