khull:sbiddle: Best advice if you buy stuff regularly is to buy a $US prepaid credit card such as the ANZ Travel Cards and load it up with money. If the $ falls to 50c you're still buying stuff at the current ~85c rate.
Careful though - some online stores will not accept prepaid cards (presumably due to fraud etc).
Use a US bank issued card instead as retailers can often tell if you are using a local or overseas card for the transaction
Proof/evidence? I was told that they are exactly like a credit card so there should be no issues whatsoever.