I'm very seriously considering volunteering for the German Technische Hilfswerk (short THW). It's a volunteer based civil protection organisation of the German government, providing technical assistance for fire departments, law enforcement and for disaster relieve.
If I volunteered I'd receive a few months of basic training, after which I'd be qualified for active duty. I'd receive a pager, and if that pager goes off I'd have to leave whatever it is I'm doing to go and assist. After the basic training I'd probably join one of the specialist units and receive specialised training with that unit's equipment (common units are "illumination" or "debris clearance"). Maybe (especially because I'm a university student) I'd receive courses in leadership and become a group leader. One of my flatmates is a voluntary firefighter, and they often work together with the THW. According to him the local THW is full of students, and because the students often leave Karlsruhe when they have their degree, they are always looking for new members.
The technical aspect would be interesting, but the companionship and leadership aspects are even more interesting. My paternal grandfather was a non-commissioned officer of the Bundeswehr (he grew up after the war, and worked his way up to the rank of Oberstabsfeldwebel (NATO equivalent OR-9)), my father was an officer of the reserve. Because of conscription he had the choice to either enlist for basic training for 18 months, or to volunteer for 24 months of officer training with full pay. He decided to volunteer and according to him, his officer training has helped him immensely for his career. He has learnt a lot about leadership and team management, and about self assurance. Because conscription has been abolished I wasn't drafted, and if I chose to volunteer for military service I'd have to enlist for 4 years or more. I wouldn't even consider that. But volunteering for the THW? That seems like a very useful experience, and also like something I'd enjoy. I enjoy helping, and this is a great way I could help people.