Really interesting question.
Backup wallets/passphrases on an encrypted drive with instructions on how to use.
The encryption key would then need to be in your Last Will and testament, it could also be written in that said wallets are opened with all beneficiaries.
Depends how much you have really.
Do not make the mistake of not doing that just because you think you do not have enough bitcoin, we do not know how much valuable bitcoin could become in the future, right now one bitcoin is already enough to buy a car in the future you may be able to buy a house with it.