The will, the living will and the document designating the surrogate who speaks for you when you cannot is on the list of prepper papers you should be able to get your hands on with one swivel of a desk chair.
You can click on this link and go to the web site. Here they offer safes for sale, but they show you what is in the construction of a safe, there are cut aways of the walls, photos from accidental fires and the contents of the safes after they were burned. It is worth the look.
Before purchasing any equipment that claims fire proof or fire resistent, go to Underwriter's Laboratory's site and look for their safety rating from the famous independent testers.