The "best" activities are the ones that demonstrate clinical exposure, community service, some form of leadership, and something distinctly you. Think of clinical work, shadowing, community service, and research (if it fits your specific goals) as the core four categories worth covering.
Beyond that core, add whatever genuinely makes you a person rather than a checklist: a job, a sport, music, teaching, a side project or startup. Admissions committees interview actual humans, not a list of pre-med boxes checked in order, and your less obviously "pre-med" activities are often what an interviewer actually remembers afterward.