The first thing I would do is to create a pdf file that compiles all the necessary information, specific and unique to your institution (study skills, pre-reqs, research, volunteering, time management, transition to medical school, major, advice, Q&A for common questions, etc). Contributing authors could be well-informed pre-meds, advisers, professors, and medical students.
Since medical students are busy, they don't want to spend time to answer similar questions from their students over and over again. Having a panel discussion will be helpful, but having a compiled package with all the information helps students ask more specific questions to mentors. This will help save the time for both students and their mentors.
Other activities could include: shadowing, visiting Anatomy lab when unused, intro to learning how to suture, opportunities to research or do small projects with medical students, etc.