I volunteered for years at rescue missions and animal shelters in both operational and administrative capacities. During this time, I was a wholesaler in the finance industry, but never could stand the corporate world. While racing from dull meeting to dull meeting, I always looked forward to my volunteer hours. Eventually, I was able to leverage my experience into a new career with an NPO.
I now work in fundraising for an organization that rescues dogs (no breeding) and trains them to be service dogs for people with disabilities. We have an emphasis on returning military, and also have programs that assist at-risk youth through the human-animal connection.
As a small NPO (less than 1MM budget) we rely heavily on volunteers. Our base is 200+ and includes everything from a volunteer IT guy to foster homes to grooming dogs. If I were you I would find a cause you feel close to, meet with someone from the organization and talk about how you can help. Smaller NPOs have very limited resources, so specialized skills you can bring to the organization are extremely valuable.
Have fun!