I forget which book it was, but Michael Crichton once wrote that the highest value density item was bioengineered medical drugs, which could have incredibly high value for just a number of cells.
That's a good one, but still, a bitcoin private key can fit on... maybe... one hundred millionth of the space of a few ounce drive? And there are already keys that have been worth millions of dollars. With more valuable bitcoin and even smaller storage of the very few bits required the potential is going to be leagues ahead of everything else.