Australian Customs and Quarantine
Australia takes quarantine very seriously, and all luggage is screened or x-rayed on arrival. You have the opportunity to declare any quarantine items, and if you fail too and are caught there is a hefty fine, and possible prosecution if the offence is serious enough. For further information, have a read through the AQIS website.
You can also bring in duty free goods into Australia, however you need to be able to show them to a customs officer so make sure it is in your carry-on bag and it is within the allowable concessions. The duty free concessions can be found on the Customs website.
For further information on what you can or cannot bring into Australia, the Australian Customs website has a lot of good information for you to read through.