Accessory:
The word accessory is French; it refers to something additional and not necessary that contributes something good to something essential. Accessory is a very broad term, applicable in the automotive industry as well as in daily needs and fashion.
In cars, extra spoilers, a multifunctional radio, seat heating, etc., can be classified as accessories.
Without these necessary accessories, the car would still function well, but with them, it’s just a bit more enjoyable. That’s what the first sentence means.