The 1993 clue referenced a brick-built pirate kitchen or galley at the expo. Some of the literature that accompanied the event had a brief storyline (I believe it's been posted somewhere on the forum), that included the food being prepared for the pirates: hot rat (!) stew, sausages and boiled cuttlefish. The sausages were on one of the teaser posters tipped me off to this.
After you told the skull those three items, one at a time, the prize code appeared.
Definitely a tricky one.