Show up at 9:00 AM in the church parking lot at Spruce Creek. I went once a few years ago. There were plenty of people gathered and I went up to someone who looked like he knew what was going on and I told him I was there to help and he set me up with bags and instructions. Take a pal so you can work together, though even if alone, they will get you involved.
We spent most of our time cleaning the access roads of discarded litter, which was palpable, and a little more time going down the trails and slopes. It wasn't that hard and we were finished with our assigned beat before noon and after dropping our last trash bags off and seeing if anything more was needed, were released to a wonderful day of fishing.
As I recall, when you got a bag full, you just set it next to the road. They had roving trucks collecting the bags. Even if you are not physically able to collect the trash, they may have a job for you if you have a pickup that can collect bags.