This will depend on whether you are travelling on an international or a domestic cruise.
For international cruises you will require a passport which must have a minimum of 6 months validity from the date of return.
For all domestic cruises Australian Government issued photographic identification such as a drivers licence or proof of age card will be required.
For passengers under the age of 18 a Medicare card OR birth certificate can be used should photographic I.D. not be available.