Seeing as it looks like you want to go down the Computing route (or why else would you really pick it?) maybe just choose Maths, Further Maths, Physics and Computing.
I doubt your school will allow you to do more, especially because they're all really heavy subjects.
EDIT: didn't see your above comment about medicine. If that's the case, pick Bio, Chem and then any one of the others. You don't need 6 nor will unis look more favourably upon you for doing so.