Maths
It depends on your school, if you have a crap school (like mine), then probably maths has not been taught rigorously and you would end up receiving the most basic HSC maths textbook available ie Maths in Focus by Margaret Grove. If you have a good school (top 100), then you would get something like fitzpatrick... which is excellent.
My suggestion (and it seams to be the general consensus), get fitzpatrick (which is really called "New Senior Mathematics") and Cambridge mathematics.
Just a note in the dificulty, Fitzpatrick is easier than Cambridge. Cambridge is probably the hardest text their is for the HSC. But if you stick at it and perservire then Cambridge will really help you in the HSC.
Also, coneros or whatever is a good text as it explains things well, the only con is that it has to be about 30 years old and the diagrams are crudley drawn at best.
Physics
Jacaranda has the best diagrams and a good introduction/standby text. For a slightly harder text then Contexts is good. And for just getting a greater and deeper knowledge and understanding i would recommend "Foundations of PHYSICS" if you can find it, or anything similar like "PHYSICS". They are fairly old text and were for when there was High school honors physics (probably comparable and similar to maths extension)... along time ago.
Chemistry
This is pretty much the same for physics. Contexts is good, but Conquering Chemistry is a good, clear, consise text.