I've been road tripping and car camping (cross country, solo and with others) for over a decade now. These are the things I highly recommend having with you.
Sections
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Car Camping
Road Tripping
Car Camping
I've car camped in my Rav4 from NY to CA and back, and many places in between.
This is what I used to make window covers. I cut them to fit right inside the window, and covered one side with black fabric.
Reflectix Roll Insulation
These rock! They are inflatable so they don't take up much space. Leave them on your dashboard to charge during the day. And they so light and can hang anywhere. Plus the frosted ones are great for in the car at night, much less intense light.
Luci Inflatable Solar Lanterns
I bought one of these for every member of my family for christmas after I got my own and loved it so much. Hang from anywhere in your car, or on your pack, or sit it on a table, stump, etc. Highly recommend.
Solar Flexlight
A power bank is so important. Charge your phone, lights, etc while you sleep. Also just safer to have a backup if your car battery dies and you need to charge anything. I also bring a tiny one that can go in my day pack for while I'm adventuring.
Power Banks - Anker US
I LOVE this thing. It's compact, easy to set up, and can either reflect the sun away or you can use the black side out which I do when it's cold out.
Auto Drive Windshield Sun Shade
Road Tripping
In addition to road trips for fun, I've worked at music festivals for years which lead to a lot of long drive across the country.
Having a paper copy of a map is so important. You can't always rely on electronics while on a road trip.
Rand McNally Road Atlas
You'll save so much money on entrance fees with a pass if you go to more than 2 parks in a year generally.
Entrance Passes (U.S. National Park Service)
When there's no place to stop for miles and you need food, these are perfect.