Coin collectors, for example. Plenty of ordinary "for sale" listings say "I'll take USD50 or two ounces of fine silver coins/bars." I suspect there's also a similar sub-economy in the apocalypse-enthusiast fandom where they're always predicting the death of fiat currency Soon (tm).

Compared to bitcoin, I'd actually argue the fiat on/offramps are easier-- most any local coin dealer or pawn shop will trade a Gold Eagle, Maple Leaf, or Krugerrand within a few percent of spot price and with immediate turnaround, and it's got plenty of well-established legal and tax frameworks around it.

Actually, that brings up an interesting question: do we know how to insure cryptocurrency yet?

If my house burns down, and my physical wallet goes with it, they'll replace a nontrivial amount of paper currency that was destroyed-- something like $500. But if the fire took out a flashdrive with the key to a BTC wallet worth $500 in it, would their responsibility be to replacing the $500 in lost value, or "here's a new 16Gb flashdrive worth $4?"