When living in one's car you want to have clothes that are versatile, easy to clean, and quick drying. Synthetic materials (like nylon, coolmax) and wool are superior to cotton. Cotton absorbs and holds moisture... its cold in the winter and hard to dry during humid summers. Most synthetics, and wool, continue to keep you warm even when wet.
I prefer clothes that are geared for hiking, fishing, and hunting, as they are designed to take abuse and to keep you cool in summer and warm in the winter. I choose styles that are versatile-- usually collared shirts that can pass for casual or semi-dressy... something I can wear to work or in the woods. Campmor is a great source for these types of things, but I only buy from their "hot deals" or "clearance" items... otherwise they are overpriced. One of my favorite finds is a fishing shirt that has a collar and can be worn with long or short sleeves. Utility pants are also useful-- the kind that zip/unzip between shorts and trousers. The synthetic materials of these items resist dirt better than cotton and they dry very quickly after washing. When travelling in Thailand, I washed my clothes in the sink and hung them to dry.... my cotton shirt never seemed to dry out... while the above-mentioned fishing shirt dried in a few hours.