Need to know intermolecular forces.
Need to know polar/non-polar stuff.
Calculations are a big part.
Need to know how to balance equations and stuff too. You should be trying to get proficient at the skills side of Chemistry.
Should know in depth about Hydrocarbons already.
Its been 2 years and I can't remember anything else that is also useful for HSC. Its possible there is more, however I can't really remember any more what else we needed.