I’m very happy to see that you’re setting your goals high, that’s very good and also really impressive. But Ivy Leagues, ESPECIALLY Harvard are extremely difficult to enter. From what I know, Harvard has an acceptance rate of 5.9%. Aside from an active school life (sports teams, clubs and activities), definitely have all kinds of job experience. Volunteer hours are important, but not as important as job experience. I know from my university/college friends that this is almost as essential as good grades. Doing well academically shows that you know how to play by the books. But having job experience or references from businesses, companies or managers shows that you can handle yourself in a workplace. It shows them that you have skills outside of simply studying and learning. As the job market is sort of crappy right now, it may be very difficult finding a job. I would suggest the following: either do a co-op program or a summer internship kind of thing. This will get you the job experience you need, the references and makes your application that much more competitive.
I wish you all the best in working towards your dream school and gaining very helpful work experience. Good luck and take care!