Chip sandwich

Clyde Langer brought in a cold chip sandwich, containing salt and vinegar, as an alternative to the rotten canteen food in Park Vale School (or as he calls it "the canteen of death"); which scared Kist Magg Thek Lutiven-Day Slitheen in his disguise as Tim Jeffery. This helped Sarah Jane Smith figure out that vinegar was a weakness of the Raxacoricofallapatorians. (TV: Revenge of the Slitheen)