I've done some research on time capsules to learn what people decide to send forward to the future inside them. I was present for the opening of one time capsule buried at the San Francisco airport, and boy was that disappointing. What I learned is that stuff we think is important will not be in the future, and stuff we don't think is important now, will be. The most common reaction to opening a time capsule is "why did they save that? Why didn't they include x, y, or Z, which no one saved?"
My theory is that we tend to collect or save things we are conscious of as having value, and we ignore the material subconscious. We are not even aware that we are throwing these everyday items away because we are not even aware they exist in the first place. We simply don't see them. Yet it is these invisible, "subconscious" artifacts that will tell the best stories about this time later on.
This is where the archeologists do their research: in the garbage pits. Here they can explore the subconscious of the lost culture.
So if you are going to collect something that you want to be significant in the future, collect things that everyone ignores now. Stuff that is too insignificant to save, that no one in their right mind would save. These "subconcious" things are the ones that will be the most valuable in the future. Not the Star Wars action figures, but the fruit stickers.
Not the Barbie doll outfits but the lids of take-out beverages.
Not mint condition Chevy cars, but bread bag ties.
Because they are not trying to be anything other than what they are -- any beauty they contain is functional -- they also transmit the subtexts of their time. The "meaning" of the placement of the ridges and holes in the take-out beverage lids reveal all kinds of things about how and where these beverages are being sold and consumed. The designs will tell folks in the future far more about our lives today than tiny models of Darth Vader.
And if history is any guide, we'll find their functional beauty for more everlasting than the fashions of more conscious designs.