Sounds like you are already volunteering (good for you) and continuing that can give you a wide variety of experiences, but you can also get a job and choose volunteering opportunities which are flexible. I've found a variety of volunteer positions, like this one, which can be done whenever you have the time. There are also many one-time events where you can gain exposure to many different organizations and you could target those relating to your future career.
With every good wish -- and keep on volunteering!!