My son is 22 mths and we got nothin'. Until he's old enough to self-occupy I think we are doomed :-( We try to go at nap time in the hopes that he falls asleep (maybe 1 out of 5 times) but other than that it's stress the entire trip.
Now I just tell him 'mommy can't turn around when she's driving, sorry' and leave it at that. He cries and carries on but we need to get to our destination safely so I need full concentration.