Popcorn was a type of food.
The human forms of the Gods of Ragnarok ate popcorn at the Psychic Circus. (TV: The Greatest Show in the Galaxy [+]Stephen Wyatt, Doctor Who season 25 (BBC1, 1988-1989).)
Pete ate popcorn while watching Frankenstein on television. (TV: Doctor Who [+]Matthew Jacobs, Doctor Who Television Movie (Fox Broadcasting Company, 1996).)
The Third Doctor bought a bag of popcorn while at the cinema. (PROSE: A Visit to the Cinema [+]Vanessa Bishop, Brief Encounter (1992).)
Reluctantly settling down to watch cricket with the Sixth Doctor, Flip Jackson made bags of salted and toffee popcorn using the food machine in his TARDIS. (AUDIO: The Fourth Wall [+]John Dorney, Main Range (Big Finish Productions, 2012).)
Dorothy McShane enjoyed salty popcorn, something that the Seventh Doctor considered a failure on his part. (AUDIO: Dark Universe [+]Guy Adams, Main Range (Big Finish Productions, 2020).)
Nardole kept popcorn in his dressing gown for unspecified reasons. He offered to make some for the Pict tribe in an attempt to ingratiate himself with them. (TV: The Eaters of Light [+]Rona Munro, Doctor Who series 10 (BBC One, 2017).)
Behind the scenes
In the fourth-wall-breaking cinema intro for The Day of the Doctor, Strax says he likes popcorn because when he eats them he can hear their tiny screams. As a Sontaran he enjoys this.