Hey i can only help with some of these subjects, but this is what i would suggest:
Overall: If you know who your teachers are i would go to see them before the end of term, ask them for any resources eg textbooks. Your teachers should be one of your best resources (while mine are at least)
Japanese: I know there are many language apps online eg. duolingo so you could attempt to begin to teach yourself the basics
Legal: if you get your hands on a textbook, i would definitely start summarising, as for me legal work can quickly build up
English Advanced: You should start reading/analysing your prescribed text or bein practising creative writing (depending on what unit your starting with) Again you should see your teacher to discuss this.
Maths: If your prepared to teach your self, i think it would be helpful to get your hands on a textbook
Not sure about bio and music
There are many online sites that help you self learn a subject
Good luck