For starters, that is an absolute great idea. Particularly something in a position that would be considered an authority or leadership position such as for the Boy Scouts or your local VA hospital, Law Enforcement agency, Fire Dept, Children's Hospital, Boys and Girls Club, etc. That as a opposed to say, the homeless shelter, church yard sale, or blood drive. Not to knock those latter options but they aren't going to say "look I'm a leader in the community" as loudly. Granted, it may be equally challenging to volunteer at some of those establishments with a record, but at least it's interview practice and experience for your big "dream job."
Having refrained from illegal drugs and activity since the incident in question is good juju. Excelling in academics since that time is also good juju. Perhaps tutoring kids, or even other EMT students is a good idea. Good references from employers and instructors are well received as well. Ultimately, the hiring folk want to see something in regards to you learning from your experiences, from who you were so to speak, and transformation into who you are today. They want to see positive indicators of your current judgement, suitability, and stability.