TimTams are very good, but not unique. In England they have 'Penguins' which are in essence the same thing.
Australia is the Mecca for junk food, though:
Strawberries 'n' Creams, Bananas, Pineapples, Ruffles/Samboy Chips, Kool Mints, Redskins, Chocos, Choc Milk, the list goes on!