Australian summers can get very hot, usually up to 90 degrees, and it is good to bring cool, light clothing that will keep you comfortable in the heat. If you're going to be outdoors often, pack a hat to keep you shielded from the sun. Australian winters are mild and rarely get below 40 degrees, so pack sweaters and jeans for a winter trip. Also pack a rain jacket, in case of inclement weather, sunglasses, and comfortable shoes, for exploring or walking around.
Of course, if you are going to the outback, you will experience temperatures considerably hotter, up to 110 degrees. Because many parts of the Outback are desert, these areas get very cold at night. You might be facing 30-degree weather at night after a 90-degree day. Parts of the south and the alpine regions can also get very cold. Make sure you pack the appropriate clothing, and a tent or sleeping bag if you will be camping. Most Australians dress casually, so a lot of fancy clothes aren't usually necessary.
Customs will allow you to bring your laptop into Australia, so bring it along if needed. Make sure to pack a converter for any items that will need to be plugged in. You will need an adapter too, as Australia uses 240 watts for electricity appliances. Bring standard personal items such as hair products, toothpaste/brush, makeup, and razor. Insect repellent will be helpful for outdoor activities. Sunscreen is a must, as the thin ozone layer in Australia enhances the sun's potency.
You can bring up to 250 cigarettes, 2.25 liters of wine or spirits, and up to $900 of general goods. Australia's customs site identifies general goods as "gifts, souvenirs, cameras, electronic equipment, leather goods, perfume concentrates, jewelry, watches and sporting equipment."