I too got turned away at Maccy's in Penrith the other week. It was 1am... I asked (waved a tenner) at the driver of the car behind me, who bought what I needed.
For my next 400km I'll be taking a stove, gas and some noodles. A cemetery/garage should supply the water and I'll crawl into a bivvy to keep warm as it boils. Not ideal or speedy, but certainly self-sufficient.