Go wine tasting
Australia has many "wine regions".Some of the most popular are:
Hunter Valley, NSW
Granite Belt, Queensland
Claire Valley, Victoria
Barossa Valley, South Australia
Coonawarra Region, South Australia
Margaret River, Western Australia
In each of these locations you will find 15, 20 or more wine producers of different sizes and most all will have a "cellar door" where they offer wine tasting and sales.
90% of the wine tasting is free and has little obligation to buy any wine.
You will typically be asked to try all the wines even including a range of Reds, Whites, ports and house specialties.
It may seem a little impolite not to purchase something, but a "Thank you" and comment like "These are not quite what I like" - will do it. Wine industry professionals appreciate that people's tastes are particular.
Be sure to have someone in your group reasonable for driving and not drinking, you can have a great day out (or two) in each of these regions.
There are often tours in each of these regions and for the best value / cheapest day, you should make your own way.
Related Links:
Hunter Valley, New South Wales
Barossa Valley, South Australia
Granite Belt, Queesland