Shopping List: A form of sheet metal, (galvanised steel etc) an engraver a pencil and ruler and an hour or so.
Transfer your coins to a paper wallet that you have rolled offline, engrave the private key onto the sheet metal (store in a safe place until needed). Destroy the paper wallet once you have verified what you engraved is what you intended to have engraved.
Yeah, that metal idea is a pretty good one. I actually have a steelwallet that I got when I bought my ledger, and it's a pretty solid way to store seed words. Those are way too expensive IMO, however.
Ages ago the SexCoin community stumbled upon a trader who was creating jewlery with QR codes etched/printed on them for persons collecting payments but not needing to cash out immediately - more practical than being handed cash for services about to begin then being robbed of that cash later on.
https://www.etsy.com/market/qr_code_jewelry
Even better, easier and cheaper, is to buy a piece of normal cheap PVC pipe used in waste water systems.
Carve your private key or seed words to that, and bury it somewhere where no-one will be building new buildings or anything in the future. Preferable to your own land or your relatives land

I'd always be concerned the pipe would be crushed or melt or some other calamity befall it.