First and foremost:
-Check visa requirements.
-Check vaccination requirements.

Luggage.
Carry on bag: The basic stuff you'd need to survive decently (a change of clothes, your documents and money is the least).
Check-in bag: Everything else
Big backpack or not?
Depends on a few factors.
How long you're going to walk with it? Carrying a full 70L backpack is tough and it's not recommended to carry more than 10% of your weight on your back (unless you're a /fit/ trainer).
Also, a 70L backpack must be checked in, you won't be able to carry that as a carry on bag.

Can't help you with money. Don't know how easy it's to exchange AUD there, but depending where you go, you can easily pay with credit card so check bank rates for foreign purchases.

For train trips/tips for around the world:
http://www.seat61.com/sitemap.htm

>>1113415
Get vaccinations and visas, that's the first step. Don't just stick to the requirements to the letter with vaccines, some diseases are common and unpleasant enough to warrant getting them out of your own free will. Malaria prophylaxis too - most importantly bite prevention, pills are up for debate.
Get a backpack if you'll be moving a lot, it's better than a suitcase for that, especially if you won't be renting a car.
Money - personal preference, but I like having cold, hard cash. I keep it hidden in a trillion different places so in case something gets stolen or I get mugged I lose only a small bit of it. I'm not sure how easy it is to convert AUD in SEA, can't help you there. Though I imagine it shouldn't be that much of a problem considering relative proximity and stability of the currency. Never change money at the airport - nothing more than you need to buy a bottle of water and a sandwich. Their rates are a robbery. Banks are usually shameless robbers too. Just look for a money changer out in the city with decent rates and no commission.

>>1113415
You will almost certainly need a visa before you arrive in Vietnam, check for the other places.

>>1113415
There are tons of pages out there for all the basics about backpacking as well as basic info about the countries you're visiting. I'd recommend checking those out, particularly read about things like must-see sites and common scams. SE Asia is very safe but there are tons of people who will try to scam or overcharge you (mostly in tourist areas, outside tourist areas less so). As long as you do your research you'll be fine. I'll throw out a few things relevant to where you're going and backpacking in general you might not pick up from a quick google search:

Get a little bit of local currency before you go in case ATMs are busted. Aside from that you can use your card to get local currency from ATMs once you arrive. As long as you have a Visa card or Mastercard from a big bank it will work nearly anywhere. I used my Westpac debit mastercard and had no issues. For security don't keep too much money in the withdrawal account in case your card is stolen - use online banking to transfer as needed. A backup card is a good idea. I also like to keep $50-100 US dollars hidden somewhere for emergencies. Some people on /trv/ talk shit on money belts but they are a good idea for wearing in transit (e.g. on trains) or if your hotel has poor security. You don't have to wear it 24/7.

Gear-wise, you don't need to take too much where you're going. It will be hot as fuck so bring cool clothes. You only need a few pairs of pants/shorts but plenty of shirts will enable you to not smell like shit without needing to do laundry every other day. Unless you see yourself going to nice places at night you should be fine with a pair of thongs and one set of sturdy walking shoes - having to carry shoes in your pack is annoying. Realistically you won't be walking that far with your pack on so size doesn't matter much, although for this kind of trip 45-60L would be plenty for your needs. You don't need any cold weather gear other than maybe a jumper for bus rides with cranked A/C.

>>1113472
Carry on should be all your valuables plus anything you might need for the transit. If your pack is out of your sight don't leave anything valuable in it - many people get shit stolen from their bag when they stow it under the bus. Padlocks are good to stop people reaching into your bag on crowded trains but a thief can pick/break it in <30 seconds so don't rely on it.

Vietnam train rides are pretty comfy. For day trips buses are better value but avoid night buses. You won't sleep with the constant swerving and honking. Sleeper trains cost more than buses but you can actually get a decent sleep so very worthwhile.

Learn a few words of the local language and be respectful to locals - you are a guest in their country after all. Bargaining is standard practice in markets and some other places so a merchant quoting you a high price isn't necessarily trying to rip you off, the initial astronomical offer is standard bargaining practice. Don't pay ridiculous prices for things as it drives up prices for future tourists and prices locals out of the market, but at the same time don't be that guy who bargains for half an hour trying to save ten cents. Bargaining can be fun if you take a good attitude and it's usually not difficult to arrive at a price that is reasonable for both you and the seller. Sometimes in tourist areas you get someone who just won't budge because they know they will be able to get the high price from some other fat stupid tourist later that day. In that case just move on to one of the 15 other vendors selling exactly the same Chinese goods.

take a pouch, mosquito net, life straw, small hunting knife, dont take too many clothing items as you will find you can just buy things cheap.

You will need solar power charger and im invest in some good sun glasses, local people dont give a shit they just want money thats there end game,

>>1114150
this is total shit

>>1113415
stay in hostels or cheap hotels; whichever you feel more comfortable in

keep a line of communication home

pack light, and by that I mean don't bring books, more than three pairs of shoes, tons of clothes

we used credit card, and withdrew local currency in bulk
we also had a reserve of USD, but we never used it

don't hire a bike if you can't ride a bike, it's not the place to learn unless you are staying for an extended period of time

keep away from all drugs, there are a number of corrupt police targeting Australians in this way
they will pay a dealer to sell to you, then they arrest you and demand cash

I found a large backpack and a daypack to be best, remember to get one with a cover to protect the straps in the airport baggage handling

unless you are going to rural areas, don't bring survivalist shit
massive waste of carry weight

Bring money. It's all anyone will care about anyway.