A car horn is not a speaker or anything that can be "played". It is set at a tone. While there may be an adjustment screw it has a very small range and it's not something that plays.
Unfortunately, to my knowledge, you can't, and here's why. Midi files are not music files at all; they are instructions to the midi synth in your computer to play certain tones. Because music files...
It all depends on your software for your car, if you are using a bluetooth, try seeing if they are playable on that device. Other than that just check that pack of paper you have in your glove...
believe it or not, more classical music was written for the horn than any other instrument ever. so the answer to ur question is classical orchestra and band music.
ON ubuntu* -first download the restricted extras (it has all the codecs u need) go to you terminal and type in: sudo apt-get install ubuntu-restricted-extras-then if u want a music player to play...