The roadster got all the press, but the Falcon Heavy's dummy payload had a tiny additional payload, a digitized copy of Asimov's Foundation Trilogy etched onto a quartz disk designed to endure for millions of years.
Stephen Wolfram, a project advisor, provided a long reflection on the challenges of leaving a meaningful memento for an unknown posterity. It is hard enough for us to figure out what ancient human civilizations had in mind.
He describes the artificial structures most conspicuous from space, and the difficulty of distinguishing them from natural features.
There's a long critique of the various artifacts and messages already sent into the cosmos, including many important signatures, dirty doodles, Lego toys, and a memorial sculpture "strangely reminiscent of the figurines we find in early archaeological remains."
Radio messages were beamed out, receiving no response, like lonely Hubski posts.
(Somewhere on Hubski, long ago, I left a comment with the Arecibo message in binary, which also got no response, and I am unable to find it now.)
So what should we send? Wolfram suggests that we might send a copy of Wolfram|Alpha, perhaps shedding light on the article title "Showing Off to the Universe." But he has plenty to show off: among the many browser tabs this article generated was a long footnote from A New Kind of Science which reminded me of a never-published trip report.
perhaps we have both been ponderously making our way through gwern's end of the year newsletter
or perhaps not
anyway, wolfram won me over as a writer with this post, the interest per square inch quotient was off the charts