i'm in year 10 , still getting using to this new system which is very frustrating btw.
But buy maths edexcel higher level 9-1. you can also try going to collins connect.
and if you go on my maths there are videos for the new spec(2015)
As for English, i'd recommend practicing writing like analysis and descriptive paragraphs.
also starting a vocab book is probably will probably be good idea).for example, include phrases and high vocab words for both english lit and creative writing.
What i do is, before an exam i memorize a bunch of 'high' voab words and phrases(depending on the task) and write it down the side of the margin and tick them off as i use it. Also, just practicing and looking at past questions or new sample papers for the core subjects will prepare you and give you an idea on how tough it's going to be.
For science, i am currently using 3 aqa science longman books (bio,chem and physics)..I;m not sure if they will be totally useful to you though.You can also watch mygcsescience videos.