I personally find past papers as the best resource, as it better replicates the sort of questions you will be asked in the exam, and how they will be asked, plus mark-schemes which will give you an insight on how to answer the questions and what the examiners are looking for in responses.
Presumably you're going into year 11? Dont do too much because honestly all year you will be so busy and wont get this opportunity to do nothing for a whole year But I recommend if you're doing a language start learning/revising the vocabulary now. And if there's anything you didn't understand that you learnt this year make sure to go over it Doing past papers is not necessary it is way too early and you probably haven't even learnt all the content yet
Vocab if you're doing MFL. Some brief notes on other subjects, only if needed though, and maybe occasional reading of revision guides and course material.
Don't stress too much. Just enjoy your holiday, seriously. Too many people I know began revision (or pretend revision) between Y10 and 11 and stopped before the really crucial time period started. Most people don't start at this point and it's just unnecessary.