The Emms module emms-history.el makes playlists persistent over emacs sessions. To make use of this feature put this into your ~/.emacs.
(require 'emms-history)
When you kill emacs all playlists will be saved in the file given by the variable:
The file to save playlists in. It defaults to "~/.emacs.d/emms-history".
After you started up emacs again, you can restore all saved playlists with this function.
If that should be done automatically on each startup, put these lines into your ~/.emacs.
(require 'emms-history)
(emms-history-load)
Normally emms-history only restores playlists. If you want it to
start playback afterwards, you can tweak this variable.