Be sure to keep a trash bin or plastic bag to keep your interiors squeaky clean. Some tissue paper, a cotton cloth or disinfecting wet wipes would be a plus.
Dedicate some space to carry snacks or water bottles. This could be handy in case you get a little hungry on a trip or if you have kids.
Add a few drops of your favorite essential oils with 1 tbsp of salt and 2 packages of unflavored gelatin and dissolve them into a jar with 1 cup of water and let sit. Poke some holes into the lid and let the scent fill up your car with your diy air freshener.
Use caddies, bins or baskets to organize your car fluids of accessories. These also could be handy if you carry around many of your belongings. Your interiors would feel decluttered and spacious.