my Lo is 18 months old and we just come back from an holiday in California where we did long car trips. We used to leave very early in the morning 3:00 or 4:00 depending on the lenght of the trip. We let him sleep till we were ready to leave, then put him in the car seat and gave him a little snack (2 children biscuit) and some camomille. He usually staied awake for about 1/2 an hour and then he falled asleep for 3 hours.
That worked well for us.
We did that a few times, too.
Sometimes our flights used to leave at 6 am, with a 2 hour car trip to the airport.
The buggy fit in the taxi. We all got up at 2 am, got ready in peace. He would have been dressed for the journey the night before.
We just lifted him from his bed to the car, he was awake for 30 min or so and slept for another two or three hours. Drive and then airport.
Mind you, Scotty is angel/ textbook.
Then, at 7 am, he'd be starving, so a very very long breakfast which included loads of slow eating finger food junk, too) and a bottle of juice with a tiny teat hole, lol.
New books and toys were also there
Good luck