Do not choose an activity because it will ‘look good in a resume’.
You should try to get patient facing experience which can be difficult for a high schooler. Consider volunteering in a hospital, or a physician’s office in an area where you will have patient contact, even if just directing people where they need to go.
In some states those under 18 can also become CNA assistants. Do your research and see what opportunities are available to you.
It is not necessary, and can even be a disadvantage to participating in expensive paid experiences. Focus on your community. Good luck.