Admission to a top school usually requires at least one very strong extracurricular. There are a few metrics with which to think about these activities.
Is the extracurricular to an international, national, local, or school level standard? If the activity is not to the level of the school, then it is probably not standout. Is there evidence of the excellence e.g., awards, recognition, a leadership role? While most parents consider sports and music to be the classic extracurriculars, anything that is pursued with enough rigour is relevant. Starting a company, developing a charity, writing for a think tank - all of these have constituted stand out extracurriculars for past students.