I have mine written down, ad hoc in a purple notebook, I intend to transcribe it when I buy a nice black notebook which will be known as the book of doom. 
Funeral plans for me, DH, DS ( it happens his best friend died at 17)
Pension provider information
Passwords to banks, premium bonds etc.,
Telephone number for the local church (for DS and I )
Telephone number for the local crem for the remaining heathen (DH)(family joke)
Telephone numbers for local venues for post funeral lunch, probably rugby club for DH and I and if he dies young (God forbid) 'spoons for DS.
Specific pieces of jewellery and where I want them to go, (all to stay with my nieces and one non family God daughter)
When we can travel again, I intend to take this book home and have this conversation with my elderly mother and make sure to note her wishes re funeral and jewellery.
It is actually very liberating for all involved.