I'm currently in Y11 and doing Physics, Maths, Computer Science, and Chemistry (though planning to drop it, just a backup) for A-Levels.
I'm personally planning to do Seneca sections on my subjects over the summer to get ahead and make Seneca a more useful resource for when I need to revise (I have Seneca premium so can do smart learning and stuff like that). I want to carry on any work ethic or good study habits I've gained from GCSEs and not just dull my brain over the summer if that makes sense. Also, Seneca has the exact course and is a very guided way of revision, with a lot of the courses seeming almost too geared towards learning the content, so I think it might be good at explaining stuff.
Tbh I'm quite excited to learn my subjects and would start now if I didn't have to spend all my time on GCSEs.