You will likely want to get some money at the airport. ATM's available.

"No one" takes US$ in payment. So your cab fare, McDonalds sandwitch, tips, etc need to be in A$. Note the one and two $ are coins. Takes a little get used to, giving someone something that looks like a penny for a tip!!Then again, tips are faily well unexpected in many cases that we tip here. Tourists are slowly changing that.