Any friends, partners or relatives that you think might enjoy the experience. There is a long tradition of bringing sweeties and chocolate-covered stuff to meets. But see 1.3 below. Mostly you buy your own drinks. So bring money.
Fluffy toys are welcome.
The sillier or slimier the better. Pterry books, Con T-shirts and the like. Valuable recognition signals. Staff will disapprove, and may chuck you out. The more anal pubs don't like chocolate, either.