As well as the singing (I detect a common theme here) I used to keep a sippy cup full of water for her to drink/splash around/play with. This started in summer but she loved it so much I always kept one handy in the car for those grizzly moments. A change of clothes at the other end was worth the peace and quiet!

We also had this fantastic "car bar" - Like a soft foam loop with a little steering wheel on it (very cute) and she would happily sit there and drive her own car in the back...! It also had other loops on it so we could attach toys (special ones she only got in the car...!) and that meant she had something to play with and couldn't drop them repeatedly.