Volunteering allows you to explore different career paths even as you contribute to a cause or organization. Volunteers only need to make minimal time commitments and can arrange their own schedules. The experience builds your resume and impresses graduate schools and employers. Finally, as a volunteer you get to interact with people who work full-time in their area. You'll be able to make contacts and expand your professional network for the future.
IU also offers options for gaining academic credit through volunteering, called service learning. Generally, this involves taking a class with a specific focus on service in a community agency. To further explore service learning, contact your academic department and see the Community Outreach and Partnerships in Service-Learning web site.
Some other resources for finding local volunteer opportunities are the Office of Student Organizations & Leadership Development and the Bloomington Volunteer Network.