RCA Cassette Adapter
Do you have an old car that still has a cassette player? If so, I applaud you for sticking with it.
That said, this RCA cassette adapter is amazing. Put it in the cassette player, and plug the other end into your phone's 3.5mm headphone jack. Now, you can play literally anything on your phone through your car stereo.
Listen to music from Spotify or Pandora, or get navigation directions and more with ease. This is pretty much the easiest and cheapest solution ever. You're welcome.