I do not know the logistics behind the Xbox GamePass ad on the box, but there is no additional card or anything other than the car and what's inside the box.

If you only need what's on or inside the box in order to unlock that then you are good.

If you need an additional thing such as a receipt or something, then that is NOT provided and you won't be able to use the GamePass ad.

This will be shipped wrapped in brown shipping paper, with the shipping label on the outside of that.