Chewing gum

From Memory Alpha, the free Star Trek reference.

Chewing gum was a flavored Earth concoction, which Humans chewed but did not consume.

In 2364, Beverly Crusher was offered chewing gum in a Dixon Hill holodeck program, but mistakenly swallowed it. (TNG: "The Big Goodbye")

In 2375, during a game of baseball in the holosuite, Julian Bashir was confused by the notion of a food that one simply chews. Miles O'Brien told Julian that his chewing gum was Scotch flavored. (DS9: "Take Me Out to the Holosuite")

In 2377, Tom Paris and Ensign Tabor created a holodeck program of the Palace Theater complete with authentic chewing gum stuck to the floor. (VOY: "Repression")