An old-school sealed envelope in my house. Could maybe upgrade that to a bank strongbox or leaving it with a notary.
Something else I haven't seen mentioned here is a plan to transfer your work and/or clients, especially if you're freelance: who will take over your projects, and what info will they need for each client? After writing this you'll want to go over it in advance with whoever will be in charge of executing it, to ensure they understand what you've written.
All of that's in the notebook, along with the passcode for my 2FA app. But thanks for the reminder!