Hi Doogie. Great that you have such a clear idea of what you want to go into! It really says a lot about your drive and enthusiasm that you're seeking information about things this early. I have some thoughts that you might find helpful.
Does your school offer AP courses? If so, it could be to your benifit to take things like AP psych or bio. You'll be that much further ahead when you start uni, AP courses cost less than uni courses, and they only count as first-year courses, so you won't be missing much! If your school doesn't have AP, you might look into getting intro psych or intro bio done by distance through your local university. That way, you'll be able to take psych courses with intro as a prerequisite in your first year. Your school counselor should know about those courses.
When you are in university, aside from your psych courses most schools like to see at least some skill in the physical sciences, like bio and chem.
Regarding volunteerism-- this can be a bit hard to obtain in HS. I think that all the crisis help lines in the area I'm in require a HS diploma, not sure if it's the same where you are. So, that's one option for after you graduate. Many universities also have peer drop-in counseling centres that you might consider applying to. This can be good, as contacts will be live and in-person, which can be a very different dynamic as compared to phone work (that was my clinical experience for grad applications and it worked out great).
Becoming a research assistant in your first year would be awesome, if you can do it. You'll probably have to work as free labour for a prof for at least your first year, however. But, this is the best experience you can get to prep for grad school. Find a prof who's doing research in an area you think is interesting (look at their interests on the faculty web site) and try to get into the lab. Ideally, where this should lead is to substantial work on a research project leading to your name being on a publication or poster, as well as having that prof supervise your own research in your 4th year. If you build some RA skills early, then find that another prof's interests are more up your alley, you can always switch over to another lab.
Oh, and start studying for the GREs.
Do you have anything that you think is particularly neat about psychology right now? What attracted you to the field?
Good luck!
(Just kidding about the GRE studying...)