yeah i agree with the all of the above. just get all your summer work done and be organised with everything that you need for the year. i'd also add that since you have a lot of free time now, if you're applying to uni, maybe start doing some of your reading for it now? ofc you don't have to but as someone who now has coursework and additional reading around subjects piling on top of my epq and personal statement, i literally have no time for reading and im also such a slow reader. if you do some of it earlier, it will help you in the long run especially because the start of year 12, to me, was a lot calmer than the rest lol.
like the poster above, give us your subjects and specs and we can give you some more tailored advice for those subjects
edit: just remembered another piece of advice - if you're eligible for them, start looking at widening participation programmes with companies or unis that you are looking at e.g sutton trust or uniq and keep a close eye on when applications open+close because THESE ARE SO USEFUL. you can get work experience and get a taste for different subjects at uni level. if you tell us what you're hoping to do after sixth-form/college, then we can give you some advice on that as well