Hmm... Be careful with that sort of approach. Schools tend to review subject selection based on those exam results. If you don't want a hard time, I'd still try my best with them. I still studied for all my Unit 2 exams last year, even though I had a Year 12 subject, and I still did fine in both. It's not as bad as you think. Also, you'll minimise your homework load for the holidays - one of the key components of head start homework is to go over your Unit 2 exam and address weaknesses (although you should still probably do a little bit of this regardless).
Yeah the incentive to study for me is pretty much knowing that studying for unit 2 exams is going to save me heaps of time over the summer to study for my year 12 subjects!
My plan for the summer:
English:
* Read A Christmas Carol twice
* Read The Lot once
* Start writing text-responses & maybe a few short-stories for context
* Language Analysis review
Chemistry:
* Review units 1/2 material
* Go over all of unit 3
* Start writing notes, answering questions in textbook for unit 3.
Specialist:
* Go over all of the relevant GMA chapters
* Start the first 4 chapters of the Specialist Maths textbook.
Methods:
* Revise units 1/2 material
* Start the first 8 chapters.
^^ That'll get me through the summer!