Rock candy was a type of candy.
As a child, Amy Pond visited Barry Island as a child where she played the 2p machines, ate rock candy, and enjoyed donkey rides. (COMIC: Summer Wholiday)
Rock candy was synonymous with Brighton. In the 21st century, Josh told Gwen Cooper that Eugene Jones "had 'loser' written through him like a stick of Brighton rock". (TV: Random Shoes)