I just did a very small thing that people may already do several years ago: using a water bottle to buy a drink instead of getting the store's plastic cup. But I still feel good cause I gonna do the same for the rest of my life.
We had a problem with bottles... Every day somebody brings new one and when was empty it was useless. But not any more. We bought bottles for every member of our group ( with teachers) and signed it up. Now we cleaned it and we add fresh water.