Well my PS isn't a "list" of the activities, I just have the experiences in there as part of the reasons I chose medicine. I mean isn't it obvious that your most meaningful activities are the ones that influenced you to choose your career? I don't see how I could answer that question without mentioning those experiences...
Not necessarily. My PS didn't mention any of my most meaningful experiences, it was focused on personal experiences that happened before and during high school that influenced my goal of being a doctor. You'll find a lot of people who were influenced based on experiences with a family member or friend who had an illness or something.
If your most meaningful experiences were what motivated you to go into medicine, of course you have to talk about them, but your PS should not simply be a paragraph-style resume. Try to come up with a theme or focus for your PS (yes, "Why Medicine?" is the prompt and main theme, but a central theme often makes everything more cohesive). You can take one experience and make it more personal, describe what you were feeling and thinking, tying in other experiences that relate. You just don't want a PS with each paragraph describing a different activity and why it relates to medicine (extremely boring). The PS needs to flow like a story.