What can we learn from our trash? Looking at what has been thrown away twenty years ago, one hundred or a thousand years ago teaches us many things: What was valued? What was common-place? How were things constructed? Who likely owned it? How are those things (tools, clothes, other human works) similar to what we are producing, using and throwing away today?
I am no archeologist but I would venture to say we can learn many things about ourselves and how our choices today will carry over into future generations. Land-fills are time capsules.