Unless you get unbelievably bored, i'd just relax and take time off before your a-levels because by then there really isn't ever time to truly 'relax' for the next 2 years. Maybe just watch some bio/chem videos, i dont do maths so idk about that.
Check out Khan academy, allery chemistry, snap revise (good short biology videos imo), eliot rintoul. If you want to practice yourself mathsmadeeasy/physics and maths tutor**** has good exam papers. PMT is honestly a godsent when it comes to chemistry papers tho. Love it.