Run up to the fairest-skinned person at the party, and start beating on him. When he gets mad and asks why, tell him that you suspected he planned to ruin the whole shindig.
Cardinal Puff If you want American music you can play Jazz the whole time. Truly and originally American.
Have a Jerry Springer food fight, have a 1970's classic rock compilation playing, light up your house with so many christmas lights so that it can be seen from outerspace, make sure somebody dresses up like Elvis,Marilyn Monroe,Rambo,John Wayne or Dorothy. Remember to drink beer from a keg and don't forget to tell plenty of Cleveland and Aggie jokes. And try to do this with your most earnest Brooklyn or Baahstun accent. Off the bottom mate.
Hookers, and lots of them. honorable mention 1) annoying hookers in a park that won't shutup when you try to dump them in a river 2) plenty of mar1juana
How bout Root Beer? I had an Australian roomate for a while, and he refused to touch the stuff. It was kind of a running joke.
Drink Lone Star or Shiner beer (although you probably can't get that down under.) Oh, and serious question here....are all the people cool with an American themed party? I just assumed most Aussies hated the USA like the rest of the world. You've given me an idea to have an Aussie party here...I might ask you for suggestion if I actually do it.