I usally carry a very small vent mount ( ). And I also carry a small steering wheel mount ( )

I prefer the vent mount, but the steering wheel mount will work in a pinch as well, but is inconvenient with a charging cable. I carry bother in my backpack in case the vent mount doesn't work.

I use this dashboard phone holder at home, and although it's a bit larger than the other two, it's actually quite flat and would consider taking it on a trip in which I knew was going to be using it a lot: