I've been trying to find out whether I can rent a car in the US (4-5 days) using only my Australian drivers licence, but my Google foo is failing me. Can anyone enlighten me? Do I still need the international drivers licence piece of paper or can I use an Aussie licence as is?
From the US Embassy in Australia:
An International Driving Permit serves as proof of validation of your Australian state license and as another form of photo identification. However, you must also carry your Australian state license. Some rental car agencies require an international driver’s license as part of the agreement.
So legally, you don't need an international permit, but bureaucratically, potentially you may, depending on the company.
I got my international one in NZ, it doesn't cost much, so I'd just go ahead and get it - at least you'll have peace of mind.
I'm an Aussie and have hired cars in the U.S. without having an international driver's license without any trouble. I was barely 21 at the time and I was told that I wouldn't have been able to hire it if I was any younger but the Australian license wasn't an issue at all.
That being said, the international drivers license is really easy to get (I got mine from a RACQ branch in Qld) and might just help you out.