When you download a Kindle book or your favorite iTune, you do not thereby own the book or song. You own a license to access a digital version the book or song, and that license is personal to you. Upon your death, your loved ones can continue to access the files only for as long as they own your digital devices and can remember your passwords. Whether they can do that lawfully is another question. Here is a great article on this topic which suggests a possible solution: have your trust own your digital files.