http://www.examsolutions.net/maths-r.../C1/module.php This is amazing for C1 revision and it has lots of other resources for maths, including past exam question with answers explained.
About the revision, remember it's quality not quantity. Sure lots of people have already started revision and some are starting these holidays, but don't worry, it is definitely not TOO late. You have all these holidays plus 4 weeks after the holidays before maths. My advice is to do a revision timetable but don't be too precise and have exact timings because sometimes you won't be able to fit to it and your whole timetable gets messed up. What's better is doing a timetable where you allocated certain topics for a particular day and give yourself the entire day to do that at your own pace. Trust me, I've learnt that from experience. Good luck, and you can still get your As, its never too late. Just get started these holidays.
Get going with the all day revision thread