I do what dofo1 does. I picked a club in the area that I ride most. Because I am three hours away it is hard for me to volunteer. In that case I send $200 per year to the club. When I am in other areas and stop to eat, get fuel, etc. there is usually a jar for donations for the groomer. I make it a point to put $20 in the different clubs collection canisters.
What does irritate me is fact that the people that do not join a club, gripe about the trail permit prices, do not help out with the groomer collections are the first people that bellyache when they hit a little bump in the trail, and then sit in the restaurant or bar and complain to anyone who'll listen to them.