I took my kids the other day (along with some of the youth from church) and went trash picking. I was amazed at how much garbage they collected on a 1/4 mile stretch. We spent a total of 40 minutes picking up and it looked beautiful by the time we left.
The winner of the day? PEE in a bottle.
(he may or may not have smelled it just to make sure)
It doesn't take much to make a difference.