Something like:
USYD - ~96
UNSW - 89 with bonus points for performance in maths and physics, FEAS interview
UWS - ~65 with bonus points for Chem and food tech
I'm no expert on this, but my sister just started Food science at UNSW this year, so I've researched a little in an attempt to calm her down a bit about various things over the summer.
For subjects, definitely Chemistry, probably Biology, and I imagine Food Tech or whatever the HSC food...