One kind of trash I am particularly struck by is the sort of "instantaneous" trash, i.e., the trash that comes out of an activity so small on a time scale, that it is truly meaningless and avoidable and selfish. (If you have a better name for this kind of trash, please let me know.) I am talking about how at BTB (formerly Big Ten Burrito), the worker will put a burrito in a paper bag, followed the person that ordered the burrito instantly taking it out of the bag, sitting down literally two feet away from the register, eating the burrito, and throwing away the bag. I have seen this numerous times. Another example is the trash that comes out of just a moment or an event. This past Saturday was the annual Hash Bash in Ann Arbor, which left the town literally drowning in trash, as you can see here.
This touches on a previous experience I had in Chicago, as well as on some things I thought about a long time ago about why we trash - we honestly don't think about more than just ourselves or the small group of people around us.