Anything below an A* in Business (teacher has said this as I got A*'s consistently in tests and mocks throughout the course, coursework is full marks, and I was awarded the Business Performance award.) Other than that high A in RE, History or Media, or high B's in English Lang/Lit as I'm predicted A's and am taking Lit next year.
Wouldn't bother with the rest if they were a few marks from the next grade as Maths you're either right or wrong so I'd think there's very little that could shift so it'd just be a waste of money, and the others I'm not particularly bothered about.