For my GCSE's I got,
5A*s 4A's and 2 B's (I'm from Northern Ireland so I didn't get number grades)
As for super curriculars I read "What about Law?" and Tom Bingham's "The Rule of Law" I was also lucky enough to get work experience in a law firm. I think whatever you do as long as you can clearly convey your interest and research into Law in your personal statement you have a good chance of getting an interview.