The new Radio Tuner mod from Lulech23 for Final Fantasy XV on PC allows players to change the music played in the Regalia while travelling - and add their own soundtracks.
The mod is available now, is easy to use, and allows owners to download the game's soundtrack too - and official Mod Tools haven't even been made available for the game yet by Square Enix.
You can get the mod here and all details on how to use it. While there have been other mods to do with the game's music, most of which can be found here. Radio Tuner however seems to have simplicity on its side, as well as the ability to play back and export tracks without replacing them, and create your own soundtracks.
To import your own music you can choose to Replace any file, using the Tuner's simple program, with any songs of your own in most formats, including MP3. Again, for full details on how to do this, go here.
We were assured by Square Enix that official Mod Support was coming soon - although it seems fans are impatient to get started, which is a good sign for the popularity of modding for the game.