You can do internships in university research labs, which would help bolster your application to medical school. Are there any topics that interest you in particular? Otherwise, if you want clinical experience (and not pipetting in a lab), you can shadow physicians of various specialties or volunteer at your local hospital. Shadowing is an unofficial requirement for US med schools, and volunteering in a hospital is great clinical exposure.Find a basic science internshipShadow physiciansVolunteer in a local hospital
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In addition to Will's answer, some larger and academic hospitals have research internships based within the hospital itself. There are many ways to volunteer at hospitals (pre pandemic), but paid jobs that provide invaluable experience that will help you network and guide your career. These include medical scribes (often done in the Emergency Department or some Surgeon's offices) and working as a nursing assistant.
In my community, we have a charity clinic that offers internships to high school and college students that want to go to medical school. The interns serve as scribes for the providers (doctors and nurse practitioners.) Maybe your community has a similar program, It is helpful in learning about the practice of medicine and the language of medicine.