Last week I was descending a hill at the mountain bike trail and saw a Camelbak podium bottle on the ground in the middle of the trail. It was actually in a precarious spot so I stuck it in my bottle cage and watched for a cyclist without a bottle but I saw none. I brought it home, disinfected it, ran it again through the dishwasher and added it to the collection. These are $9-10 bottles, I am sure someone was disappointed to lose it as it appears fairly new. 
I also find tons of ponytail holders. These are my cat Tortilla's favorite toy so I bring them home, wash them with dish soap and give them to her. I also collect tubes which mountain bikers have an affinity for just discarding on the trail. One day I will patch or recycle them.
Amanda
2011 Specialized Epic Comp 29er | Specialized Phenom | "Marie Laveau"
2007 Cannondale Synapse Carbon Road | Selle Italia Lady Gel Flow | "Miranda"
You don't have to be great to get started, but you do have to get started to be great. -Lee J. Colan