While you will always require a valid Passport to travel overseas, in some cases you may also need an Entry Visa.
If you need a Visa for your final destination and, if necessary, a Visa for stopovers/airport transfers, it is also your responsibility to obtain these. You will be responsible for any costs that may arise if you do not have valid documents with you.
You must have an approved entry permit (ESTA) and a machine-readable passport for all travel to and via the USA.
There are special requirements to have a booked return ticket when travelling to certain countries. You are responsible for checking this with the relevant embassy for the country and the airline concerned.
You should always check with www.smartraveller.gov.au, before travelling abroad.