Something that I did from April to September was to use flashcards. I found myself forgetting basic Calculus stuff like calculating the area of a surface. So I made flashcards with theory as well as questions and revised them regularly.
I don't believe you can do very well without Abstract Algebra. Topology and Real Analysis may be ok to be neglected (I was aiming at 800, got 770 in September without studying it, waiting for October results). I am an Engineer, so those were the main subjects I have never studied. I studied Abstract Algebra from Artin (up to the second chapter only) and by the Cracking the GRE Subject Princeton Review book, this book is great but it falls very short on Ring Theory, which is important for the exam, it doesn't even mention Quotient Rings and mentions Ideals in an example exercise.