When I read this, I thought someone was about to put a joystick into their car’s radio to use it as a controller for volume and tracks, etc. Haha.
But if I can add something to help, the simplest way to try it out is if you’re using a dedicated USB flash drive, just put all your mp3s onto it without any folders. Generally will avert any problems, because the first files it will read will be a bunch of mp3 files. Likely won’t require any special programs. Just drag-n-drop on the computer, plug into your car’s USB jack, and test it out. If not, you’re going to have to read up on your car’s manual for this. We don’t know how every single car’s USB MP3 player works, but the method I’ve listed is the simplest method. And simple is good, and usually works best.
But, I’d still say burn a CD or two of the tracks you MUST MUST have to bring with you. Just in case.