Australians visiting Indonesia must have a valid passport with at least 6 months remaining validity before expiry, but for purposes of tourism, you typically don’t need to arrange a visa Australia for short trips to Indonesia. Upon entry to Indonesia, you can purchase a Visa On Arrival (VOA) which is a Tourist Visa in the Airport for a 7 day stay or a 30 day stay. Currencies accepted include AUD, US Dollars or Rupiah in order to purchase this (not credit cards).
30 day Visas purchased on arrival can be extended for an additional 30 days (with not inconsiderable paperwork, inconvenience and multiple immigration visits while in-country in Indonesia).