I have a bag that contains a change of clothes (t-shirt, jeans, sweatshirt, undies, and socks) as well as a spare pair of sneakers and winter boots, and an extra winter parka.
However the following items are also in my car (both our cars in fact): gloves and winter hats and summer hats (baseball variety), a comforter blanket, pillow, reflective triangle thingies for car breakdown on highway, jumper cables, chain, nylon rope, a wide variety of tools (hammer, pliers, wire cutters, push drill, crowbar, hand saw, duct tape, etc), various medications including aspirin, imodium, benadryl, and others, writing implements and paper, scissors, chapped lip remedy, bandaids, flashlights, spare dog leashes and harness, drinking bowl for dog and bottled water for both of us, snack crackers in a plastic container, sunglasses and reading glasses, maps and atlases, a snow shovel, re-usable grocery bags, and probably many other things not coming to mind.
When I am in the car I have a small bag with me that contains my cell phone and car keys, along with many more similar items and duplicates of items already in the car. In my jeans pockets at all times are a pocket knife, my wallet, kleenex, cough drops, money, and a couple doggie clean-up bags.
Yep, I'm a pack rat. You should have seen all the items I used to pack in saddlebags when horseback riding back in the day. Before I retired, I carried a vintage lunch box which held the usual sandwich and other food items, but also all sorts of other provisions, safety pins, flashlight, pliers, tampons (a necessity back in the day), nail files, etc. I was the go-to person that my co-workers would ask if they needed this or that. As far as traveling/vacationing/visiting, I take a minimum of two suitcases cram-packed full and a cooler of food. "Traveling light" is not in my vocabulary.