My favorite additions to my car camping set up are some DIY curtains and bug protection mesh screens!

Suction cups with clips and cloth of any kind (repurposed old kitchen towels/shirts can be the cheapest and most environmentally savvy trick!) work together well to provide privacy curtains for the car windows. You'd just have to cut them to size and cut a few holes where you'd like to clip them up. They are also super easy to pack and set up and take down when not wanted. 

To prevent condensation build up inside the vehicle it's also pretty imporant to crack a window or potentially open a sunroof if you have one. The stars might look great from below but this could be enough space for bugs to creep in unwelcomed! Some cheap mesh and velcro strips are the best defense against that but still provide that nice nighttime airflow. 

At REI, we believe a life outdoors is a life well-lived.