The easiest way to hold USD is probably by trading on a CFD...

The easiest way to hold USD is probably by trading on a CFD account or similar. There may even be ETF's or managed funds that cover this, or some other online venture.

But at the moment I'm only trusting what I can hold in my hand, so I bought my USD the good old fashioned way, by converting real AUD into real USD.

Sure you get screwed on the exchange rate by the banks or whoever, but I converted in amounts of $1000 US, and as long as I was paying about $950 AUD (including fees) for $1000 US I was happy. If it goes back to 70c like during the GFC the few extra % I had to pay won't matter to me.

I most recently got some from Travelex in the Murray Street Mall in Perth. This was only 2 weeks back and I got $1000 US for $970 AUD, this was when it was in the 1.06 range, obviously I got closer to 1.03 than 1.06 though, but it was better than the banks were offering. Travelex don't charge anywhere near the same fees as banks do either.

I'm sure there are MUCH better ways, but I like to have the physcial cash (just like my gold/silver), and hey, even if I never convert it back I will have more than enough to pay for my World Series of Poker entry in Vegas one year plus a nice hotel stay.