What do universities look for in potential medical students?

You are overloading yourself. Universities look for great marks more than anything else. However, if there is competition and students' marks are tied then they will consider extra-curricular activities. Volunteering at a hospital is great work experience for you and shows community involvement and joining clubs(Student Council, tutoring) shows leadership. That's all you need to have. The most important thing to focus on your marks and not to be worried about other activities. Also, only work if you must otherwise it is too time consuming.