Today's treasures may be tomorrow's trash, but give that trash enough tomorrows and it becomes something entirely different: an artifact.
Will it be something electronic (perhaps even with some leftover data on it) that tells all? Maybe it will be some large infrastructure project (a canal, a highway) that's big enough to make it to the future reasonably intact. Perhaps it will be a collection of items unearthed from our landfills. (Please, future generations! Do NOT look in our landfills!) Tell us what artifacts are likely to reveal the most about us to the future and why in the comments.
Image: Archeologists excavating / Mario Modesto Mata