Empty pop-up wet wipe containers make good car tissue holders
We have a couple of those flushable wet wipe containers from when my kids were toilet training. We fill them up with tissues and put them in the car. They're smaller, so they take up less room and much sturdier than a tissue box. If you happen to buy just the right kind of Kleenex and place them in there just so, you can actually use the pop top on the container, as the tissues will come right out, one after another like a normal box of tissues.