This is a specialty that everyone should pursue in one way or another. I have provided some examples of volunteer work that you can do that would fit your passion. It is important to not just do community service, but to serve your community. This means you should not be counting the number of hours you contribute to helping, but in what way you help them. It is important to volunteer for causes you have a personal connection. This allows you to invest more then just your time into helping.
In order to gain acceptance to the top universities, it is important to do more than just volunteer at a nursing home or hospital. That doesn’t mean you should not do the above, but do not do it exclusively. You need to take the initiative and start a short or long term project.
Doing “good” does not have to be limited to volunteering time. You could start a social business (not a non-profit); this would be a company that helps society, but also makes a profit. There are many investors and programs you can participate in that will help you establish such a business.
International programs are a great way to gain a worldview of societal problems, but they are often expensive. It is good to keep in mind that you do not have to do something internationally to make a difference. Anything you do with the resources you have is perfect to pursue volunteer work.