There are many ways to volunteer in Australia. Some of the prominent volunteering activities are:
1. If you are interested in law then you can volunteer at the local legal centres.
http://www.communitylaw.org.au/
2. If you are time poor you can volunteer at the local op shop, local library's english language classes for immigrants, local churches and temples, every week for few hours.
3. If you like to experience new things then you can volunteer at various festivals such as Royal Melbourne Show, Swedish Festival, Japanese Film Festival, Melbourne International Film Festival.
4. You can also volunteer to organise and administer family and work events.
Volunteering is a great way to help people, earn some good karma, get exposure to varied experiences and enjoy perks like free entries to shows and festivals.