You needn't be original or impressive, just be dedicated and truly excited about whatever it is that you do. Aim for 3 hours/wk for as long as you live in the area (think long-term commitment).
Service to the community of some kind might be a good balance with a lab job. Contact a social service agency or a member of the clergy in your community and describe the type of group you'd like to work with (kids, battered or abused women, the mentally ill, adults trying to learn to read or to learn English as a second langugage, the dying). It should be relatively easy for you to find a group that needs your help.
Having a long term commitment (not just 2 hours a week for 3 mos) and, if possible, showing leadership skills is a plus.