Recommended Revision Guide
CGP GCSE Edexcel Mathematics Revision Guide
As far as revision guides go - this is the best one that I've found so far.
I currently use this in my tutoring sessions and students really seem to have a good understanding of how the book explains things.
If you're struggling to understand concepts in your Maths syllabus - this is definintely a must.
Recommended Calculator
Casio Calculator
If you're looking to purchase a new calculator, I'd probably recommend this one.
This is actually the calculator I use when I tutor and it also is the brand of the calculator I used whilst I was doing my exams.
You'll probably find that these are the calculators of choice by schools too!