I keep a file with all my passwords to all my accounts, user name, email, all updated. My wife and daughter will have that. 6 weeks ago I had a major operation and I made sure my wife knew where all my passwords could easily be found. It is not just about digital media--though you want them to have access to that, I have lots of files, genealogy info, etc., that I want them to have access to. So probably the simplest way is to have all your account info in one safe place that provides easy access to them.
I like this older article about ebooks after death:
http://www.nytimes.com/2012/05/11/op...en-you-do.html