Hello. I'm in a sedan. I'll answer based on what has worked for me.
First off... make car maintenance your top priority. Mechanical maintenance (routines & repairs) and administrative maintenance (registrations, insurance, etc). This is general for any vehicle.
Second, determine what your nightly parking situation will be. I put together a list based on all of the reading that I did from numerous sources and videos. I rotate out and never park/sleep at the same place each evening. This is also general. If traveling, plan these ahead... and also have a backup plan if things don't work out.
Next, determine your sleeping/bedding situation... as this is the primary purpose of shelter, and the primary purpose that your car will serve. Some lucky ones can lower front passenger/rear seating and make a nice long bed from passenger seat to trunk. I am not so lucky, but I am quite short, so I was able to set up in the back seat comfortably.
Also determine what you will use as window covers. In my opinion these are an absolute necessity for both privacy and safety. I use Reflectix with a black flannel side glued on with LocTite. I find that the black flannel doesn't look obvious if shined on... and it prevents window fog.
And determine how you will handle your toilet needs. I utilize public restrooms, but I also have a backup system in-car in case of an emergency.
At this point, most people make a list of what they think they will need. If you do this, you will spend a year of misery adjusting and readjusting your in-car inventory. Instead... make a morning routine and nighttime routine... what you will do first thing upon waking and breaking down your car camp... and what you will do to park, set up, and wind yourself down. THIS will determine what you actually need in the car with you. You will still make adjustments along the way, but it will be far less miserable.
Everything else you own can either go in a storage unit, or you can get rid of (sell or toss)
The rest... some food, eating utensils, hygiene items, a few sets of clothing, cleaning products... can be sorted out as you go, both in what you will keep with you, and where these items will live. I keep only non-refrigerated foods, and those go in a crate on the rear passenger-side floor. A basket with plate, cup, and utensils goes on top of that. I have a zipable clothing pack on the rear driver-side floor. A plastic basin goes on top of that with a washcloth, dishcloth, handtowel, vinegar spray, water spray, bar of soap, and overnite bag. In my overnite bag I have toothbrush/paste, and etc.
In the front passenger floor is my battery bank, and on the front passenger seat is my office/work items, which amounts to my computers and a small file box.
I keep the entirety of the rest of my household possessions in a storage unit.