What does "Throw Another Shrimp on the Barbie" really Mean?

The phrase was used by the actor Paul Hogan (Crocodile Dundee) in a 1980s TV commercial which belonged to an advertising campaign by the Australian tourism board aired in the USA. The use of the word shrimp was because an American wouldn't know what a prawn was.

You won't find the word shrimp in spoken Australian English but the word prawn. Besides, barbie is the short form for the barbeque.