Werner asked for a small Mp3 player with display that can show a basic chord/melody line on its screen.
I think, using MP3 album cover graphic could be a solution.
Album covers are stored in the ID3-Tag of a MP3-file. Son create a cover with basic song information, showed on the players display when playing the MP3. There are several ways to do this.
Created with MS Paint:
Created with BIAB, using chordsheet->Preview->save as jpg dialog:
Ralf