Advanced English: Nothing specific - but Yr 11 studies should have enhanced your overall ability to comprehend, interpret and evaluate texts and to synthesise your ideas in a composition with sophistication.
Maths (all levels): Absolutely everything you've ever learnt through K - 11 is essential.
Biology/Chemistry: Everything in the Yr 11 course is assumed knowledge. Although no question in the HSC would be specifically directed at Yr 11 content, this knowledge is needed in order for you to effectively explain/evaluate aspects as required by the Yr 12 course. The following is a (very-very-brief-off-the-top-of-my-head) outline of the core topics in the Yr 12 Bio/Chem courses and their relations with the Yr 11 course. Others are welcome to correct/contribute.
Biology:
9.2 Maintaining A Balance mainly deals with how and why organisms maintain a stable internal environment and function in response to variations in the external environment.
Need to know from Yr 11: Some of 8.3 Patterns In Nature, including transport systems in animals (esp. excretory system) and plants (phloem/xylem), active/passive transport, etc.
9.3 Blueprint Of Life mainly deals with the variety of evidence that supports Darwin/Wallace's theory of evolution, the mechanisms of genetic inheritance, the implications of genetic technologies, etc.
Need to know from Yr 11: Some of 8.4 Life On Earth & 8.5 Evolution of Aust Biota, including examples of evolution in Australian flora/fauna, processes of mitosis/meiosis, etc.
9.4 The Search For Better Health mainly deals with the components and functions of the human immune system, a variety of infectious/non-infectious disease, the strageties used to prevent diseases and their implications, etc.
Need to know from Yr 11: Some of 8.3 Patterns In Nature & 8.5 Evolution of Aust Biota, including components of cells, processes of mitosis/meiosis, etc.
Chemistry: I don't have time to go into detail as I've done for Biology. All HSC cores revisit and extend the knowledge you've gained from the Yr 11 course, e.g. chemical formulae, chemical bonding, moles, intermolecular forces, enthalpy (exothermic/endothermic reactions), carbon compounds and their nomenclature (alkanes, alkenes), factors that affect rate of reaction, etc.
9.2 Production Of Materials mainly deals with the production and uses of petrochemicals and the development of renewable replacements for petrochemicals.
9.3 The Acidic Environment mainly deals with the uses of acids and bases, the chemitry of acid/base reactions and the environmental impacts of acids.
9.4 Chemical Monitoring And Management mainly deals with the monitoring of chemical reactions in industries for the purposes of maximising profit and minimising adverse environmental impacts, the uses and implications of analytical chemistry in managing the environment.