Ironically it's probably putting it on encrypted usb stick in a safe vault of a bank containing your private key or a wallet.dat with a password. I say ironically because bitcoiners were famously against banks. At least some were. Or instead of usb, you can use that metal keycard you talked about, or Ledger nano X or
Ledger Nano X or Trezor.

Carrying them yourself is just dangerous.

Or you can do what Vitalik did with his wallets. He gave half of the privatekey of one of his wallets to his father. I see that as risky.

My way is against crypto ethos and i am storing mine in a trusted exchange. I see way more plausible that i would lost it if i guarded it by myself.