First of all, much of what you do as a high school student cannot be counted towards your medical school application.  Medical schools are looking to see what you have done during your undergraduate and post-graduate years.  As a high school student who is interested in pursuing medicine, what can you do?

1. Volunteer at a hospital.  Ask your local hospital whether there is a volunteering program for high school students.  Many of these programs have you helping patients by delivering them flowers and gifts, bringing books and magazines, wheeling wheelchairs, etc.  The benefit is that you can also have the opportunity to interact with physicians and nurses and learn about the profession and learn how to interact with patients.
2. Volunteer at a retirement home.  This is a great opportunity to learn how to interact with people, especially geriatric patients.