Airlines look at the weight of your luggage more than the physical size, though there will ultimately be a limit on size anything you can carry on your person will usually be acceptable. Find a way to go with light travel options. A light suitcase is a good start.
Try to keep the number of electronic devices to a minimum. A smartphone or tablet that takes photos will serve most of your needs.
Of course you smartphone may not be connected to a system overseas. Talk to the provider beforehand. Consider renting a phone overseas, or using your regular smartphone with a rented sim card/account.
Foreign countries will almost always have a different power system to Australia, meaning that virtually all our devices from home are useless. Don’t be fooled by power adapters, they change the plug but not the voltage, so the electrical equipment still won’t work in most foreign countries.
Cameras, iPads and anything with a USB port can be charged from any USB charger. This is one fairly universal standard. Take the right USB cord and either buy a USB charger at the destination or make use of the USB port on the television or other device at the hotel.
AA batteries, used in cameras and disc players, are standard and can be bought in most places. Other internal batteries in electrical devices vary between manufacturers. They may be hard to obtain overseas.
Have a few portable USB chargers/ powerbanks for all your devices, It is terrible if the camera has no power and you want a photo of your vacation.
Cheap USB players (literally a few dollars) can be bought online. They use a SD memory card for storage. Buy one for the trip, and just keep the memory card.
A good set of headphones is an investment. If you travel often its worth buying noise cancelling headphones. These get rid of the background rumble of the plane when you fly, giving you a peaceful and quiet experience. They are pricey, and will consume battery power, but they are worth it if you use them on a regular basis.
Be careful buying electrical good overseas. If they are designed for foreign power systems they may not be compatible with the Australian electrical system. Anything that uses a plug pack can probably work if you buy an appropriate plug pack in Australia. Other larger devices can sometimes be switched from 110volt to the Australian 240volt by a switch near the power cord socket. Check before you buy.
Take a Sydney airport shuttle and avoid the hassle of public transport and concerns with luggage. Sydney airport transfers are on time, every time.