GCSE bitesize does not work at all for me, but I saved up some money from working as a waitress and went all out at WHSmith! Honestly, I paid £10.99 for a "filing book" - sounds like a lot, and it is... but it's so worth it! Education should not have to compromise, it's got thin ruled lines and margins and the pages are so beautiful... sounds odd but it's the biggest motivator I've yet had to revise. I now find myself wanting to get out a pack of highlighters and go crazy! Drawing also helps me with revising, I'd recommend getting a good revision pad that you can divide up with a few subjects and really work hard.
MATHS:
I "borrowed" (effectively stole considering the school don't know, although I shall return it soon!) this big text book with questions labelled "D/C/B/A/A*" and I went through the exercises and wrote out notes in a new maths books and have filled up about a hundred pages, but it's helped so much! In class i'm so good now, start early guysss - best advice!