I envision a book that on would write at any moment in life. It would have different chapters, like :
- the most important moments in my life,
- the people that helped me become who I am,
- the persons I am thankful to,
- my best memories,
- the places I like most,
- my little pleasures in life,
- the values that are fundamental to me
- the misfortunes of my life and what they taught me
The book wold be written by anybody - even in a perfect health condition - and reviewed regularly to add to each chapter and change things. At the beginning, there would be a list of people who would receive it in case of an accident or after one's death - with a specific chapter dedicated to those specific persons (like "why I loved you", "what I wish for you", etc.).
And as most people would be willing to have these books written while they are already sick and maybe unable to write them themselves - this initiative would also require a network of volunteers to spend time with old or sick people and listen to their memories.