I've said this before and I will say it again. Don't spend everyday doing work during this holiday. You need a break to relax or you will suffer from burnout - so do anything but work and have a bit of a life. If you really want to, do a little bit the week before you go back, recap some topics probably. I'm an A2 student, followed my pattern above and came out with AABC at AS(grades I was happy with, despite dropping c-graded chemistry!)
Back to chemistry, its a tough subject and you will either get some concepts or you just won't. Go over them as much as you can and try and stick it out and if you want, drop it after AS. For courses like Biomed/Biological sci, it is true that quite a few uni's don't need chemistry (mainly Biology and another science), however like someone said above, there will be some Chem based modules and if you do chemistry at least to AS, it will benefit you. Sometimes uni's may consider you more if you have chemistry at least at AS, even if it isnt in their requirements