I donate to the PCTA.
I maintain a website about local trails and on it I post Volunteer Wilderness Ranger reports. These reports are sent to me by a local ranger and feature volunteers who have gone out and done trail maintenance or evaluated the conditions of the trails. I got an award for doing this last spring although to me it seems like nothing, but I guess they didn't have a way to make these reports public so I provide that.
Sometimes I do volunteer wilderness ranger trips myself as a participant, not a leader.
I sometimes do unofficial volunteer trail maintenance on "non focus" trails, which are trails the Los Padres forest kind of turns a blind eye to, expecting that they'll just melt back into the forest.
I lead Sierra Club hikes and am a member.
I don't do a lot of trail maintenance. I don't really like doing it much. I also don't donate very much money. I find you get on too many mailing lists if you donate. It's super annoying. I think they make more money selling your name and contact info than they do from your donation so until they stop doing that, I only continue the memberships I already have and want to keep but not donate to every cause or join every organization.