As opposed to renting a safe deposit box at the bank to store your wallet information, many banks offer a 'secure document' or 'secure packet' service where they only store an a4 envelope of documents for you at a much cheaper cost. You can use this service to store details of your wallet information, but also copies of your Will, any power of attorney documents, your passport and your insurance policies as well.
You could then leave this packet to your heir in the event of death, or alternatively you can arrange for your heir to be able to sign the packet in and out of the bank by themselves - this might not always be the best option, but if you've got unconditional trust with the heir (for example, my wife can sign out my packet, but we also have joint bank accounts and live together so it's not like she wouldn't have access to my information or assets anyway!).