Hi, I'm a current Year 10 student. It's not necessary that you do any substantial work over the holidays for any of your subjects really, however i would strongly recommend revisiting everything relevant to your GCSE course that you have learned in Year 9. The only reason i say this is because the workload only increases from now on. Don't stress yourself out though, just make sure you understand your science topics, in particular, to a high level to really cement the key processes in your brain. A few maths questions a day to keep your brain working too maybe. You'll only be helping yourself and (believe it or not) reducing the workload for yourself by the time it comes to topic tests/ mocks. And by revision I don't mean past papers specifically, just write comprehensive notes (if you haven't already)/ flashcards (if they help).
Something i wouldn't recommend doing is getting a headstart on your extras. Your school has already started you off on the core subjects, most likely because they are the subjects that requre the most work/ memorising/ learning. That's not to say a little precocious reading will harm you, just make sure you prioritise your core subjects if you intend on doing any revision in the holidays- which i will repeat is not at all necessary!
As far as Year 10 life goes, I'll be honest it's quite fast moving for me personally. The content can be enjoyable, just make sure you listen to your teachers and don't muck about (I'm guilty). Topic tests will come and go, you'll stress about them at first, but will then learn that they're really just consolidation tasks to help you.
You clearly have a good work ethic if you're planning ahead in Year 9, and so my advice would be to maintain that throughout the next two years! Good luck, and enjoy yourself as much as is possible!