alt Hacker NewsDifference is a plastic card that is lighter and smaller than the phone is just as effective as the phone is for payments. When it comes to audio, a car stereo is going to be much more convenient and brtter quality than a boombox or bluetooth. That said, i did know someone with an older car who used a bluetooth speaker instead of their stereo, so they could connect their phone audio.
I don't know about where you live but here contactless card payments have lower limits than phone-based ones. Also the phone allows me to switch between multiple cards, including transit-specific cards.