Super-curricular help for economics

Currently studying in AS level (y11), right in the middle of it. I want to get into a top UK university, which I know sounds pretentious but I do really, really want to study at Oxbridge. Probably going to take economics, or a related course. Grades are the most important, especially for UK universities, but since some extracurriculars and super-curriculars are needed too, I’m not sure what I should do. For extracurriculars, I do write quite a lot, and do art pretty decently (which I have a very small insta page for), but I need to know what else I should do to almost guarantee an entry? One thing I know I should definitely check out is economics related courses. Thank you!