When I was in Y10/11 (years ago, lol) all I remember doing in the holidays, other than Easter right before the exams, was getting up to date with coursework. I think unless you're ridiculously behind, it's just as important to chill out and relax as it is to do anything else. There's still plenty of time to work hard, and if you do too much too soon you'll burn out before the exams.