Turn the ac on and roll down the windows.... a car out in the sun can easily get to 150 degrees... so use the ambient air to get back to the outside temp... and it takes a minute for the ac to get its pressures up to snuff...
From everything I have read ( in addition to last posts) window tinting can make a lot of difference.... and particularly on the moving green houses.... I mean the wagons....

Does anyone have a car cover they use out in the heat ?

One could just fit over the cabin area on a sedan and make a lot of difference... and be light enough to throw up there without much tying down....

I am thinking of making a cover like that...