Stick an old phone into their pocket/bagpack, sim ideal but not required.
Connect that phone to your phone hotspot, so you can turn on your hotspot and, if the phone connects, it's nearby plus you can use Find My to track it from there, play sound... etc.
Bonus if you have access to e.g. XFinity or whichever is the most prevalent free wifi around, so your phone can come online occasionally.
Oh it's absolutely a hack for the better-than-having nothing scenario :)
My main issue was remembering to charge the old phone every few days as I'm not in need of this regularly, so more of an occasional thing like to an unfamiliar place/country, or on a trip to Disney.
Connect that phone to your phone hotspot, so you can turn on your hotspot and, if the phone connects, it's nearby plus you can use Find My to track it from there, play sound... etc.
Bonus if you have access to e.g. XFinity or whichever is the most prevalent free wifi around, so your phone can come online occasionally.