It's an airline provision and will vary with whichever airline you use.
I think Qantas and perhaps Luthansa, and maybe Singapore Airlines might have most generous arrangements and it is not so much published on sites but have seen reports you need to ask.
I am a traveler and I am not a migrant to Australia, is there a baggage limit for travelers like us because me and my girlfriends are gonna be traveling Hong Kong 3 nights, Sydney 5 nights Coffs Harbour 7 nights GBR area ( undecided on where to stay) and finally Singapore 4 nights this coming November. I have a many stuff and I don't have a nice luggage or trolley here in our country. I will be carrying 3 big bags with me and seems that is so uncomfortable for me to travel. I want the feminine side of me and I am looking for a pink luggages that I want to buy in Australia together with my friends. Please let me know here what brand name of cases/trolleys/luggages to buy or where to buy in Australia. Any tips for what we need to pack also how do we organize the packing it seems daunting all that packing & unpacking!! Which should i bring suitcase or backpack?
Samsonite is a renowned brand though very expensive and they have a sexy hot red one you'll see @ Bagworld Australia | Samsonite, Guess, Antler, Blackwolf, Bags, Luggage, Suitcases, Laptop Bags, Backpacks and also @ Luggage Direct where you have a purple and again a Samsonite hot pink trolley traveller bag.
In Sydney, you have to check out the Queen Victoria Building as well as The Strand and all that area for some good shopping but I'd expect that whatever Sydney has, HongKong will have also and quite possibly a lot cheaper.
I'd certainly buy before you leave, either online or from your stores.
Whether it's a trolley pack or a backpack is really personal choice but if you are just travelling to various accommodation centres with door to door transport you hardly need a backpack.
An alternative to the upright tolley ones are the Blade Runner horizontal bag or wheeled duffle as they can be called - Luggage Store - Home : LuggageStore though probably not too many about in your pink desire.
Colours aside, I personally find the best for convenience these days is to have a wheeled duffle and then consider getting yourself a sizable daypack in which you can carry things you'll use during the day but also not so large you cannot take it aboard an aircraft as cabin luggage and also to have any valuables in along with basic toiletries and a couple of changes of clothes just in case your main bag gets displaced and uless you are planning in the future for a lot more of off the beaten track travelling a back pack is hardly needed.
In addition to a daypack as cabin baggage, you will also usually get a way with having a smaller big handbag style bag which can also no doubt be handy for a female travelling.
November is going to be getting into warmer weather and with a lot of rain we have already had, humidity will be higher, not as bad as Singapore always is and HongKong no doubt often but you will likely not need any bulky clothes and lighter casual things, Shorts and simple tops is the go for theday and a couple of nice dresses just as you might wear of an evening back home or slacks or whatever.
But do the exercise of laying out what you think you might like to take and then halve it and you'll have about the right ammount and then probably have room for buying stuff as you travel, Tshirts with something about where you are being a good useful reminder of your trip.
You also ought to get yourself a good summer hat to protect from the Sun and in Sydney get to a store of Shop - Australian Geographic as not only do they have some interesting Aussie theme type stuff but look for a collapsible mesh hat [ ask a shop assistance ] as they fold up to fit in a pocket and only weight about 100g.
Only come in one colour and that's black but you could always ass a pink hat band.
Buy yourself some tropical strength insect repellant and a good strength sun protection cream for our southern sun can be stronger than what you are used to.
If you have not yet booked your accommodation and travel for Coffs Harbour or can change it without too much additional expense, I would consider getting to Byron Bay instead for a couple of days and then on to the Gold Coast before the GBR.
The GBR btw stretches over about 2000 km. and is not a continuous reef but a series of reefs and islands that you can even access the first of from not too far north of Brisbane.
If your budgets allow, have a look at the four day/night packages that include Fraser Island you will see under Bookings > Packages pricing on Lady Elliot Island Great Barrier Reef - Official site
Something like that may work out better for you depending on where you fly to Singapore from.
If you are leaving from Cairns you could head further north and think of a couple/few days at places like Great Keppel Island and/or The Whitsundays - Whitsundays - Home and make sure of getting to Whitehaven beach and if possible do a sailing boat cruise for a few days.
If you have to return south for a flight out you can still fly from either Hamilton Island or Proserpine.
But best to keep your baggage as light as possible to save paying for excess baggage and you may anyway find you spend mostof that feminine time in beach wear and not much else.