According to N.Y. Times article Bequeathing the Keys to Your Digital Afterlife, Google has a program called Interactive Account Manager. This feature allows you to direct that Google deactivate all related accounts after a selected period of ‘silence’.
Also, other programs such as SecureSafe allow you to store username and password information. In fact, I would expect that these types of apps and programs abound.
Or, as the Times article points out, there’s always your sock drawer. Not that I’d recommend it.