Glad you mention this, Jack. After working for the Appalachian Mountain Club and Green Mountain Club for several seasons over the course of several years, I've seen just how much membership dues and donations support the trails that non-profits and other clubs maintain.
Up until a few weeks ago I never paid for my memberships to the AMC or GMC because I got complimentary memberships for working for them. I've let my AMC membership lapse because I don't care as much for where their money goes. I just became a member of the Maine Appalachian Trail Club, the PCTA, and the Cohos Trail Association, and I'll be renewing my membership to the GMC, all because I love the trails these clubs maintain, I think they do good work, and I think they could use the money wisely.
When I can, I do trail work, but not having a steady job or schedule, it's hard to devote time to volunteer trail work. Money is the other good way to support the trails you love, I think.