The Oz National Anthem, "Advance Australia Fair" is one of those that is interchangeable with Amazing Grace, House of the Rising Sun, Gilligan's Island etc. It's especially fun to sing either of the serious ones to Gilligan's Island.

*goes off singing*    Australians all let us rejoice
                              For we are young and free,
                              We've golden soil and wealth for toil
                              Our home is girt by sea, our home is girt by sea....