For me it's no eating in the car. Hard stop. I don't care how hungry you are or how much of a hurry we might be in. We can stop and get cooked food and eat it before continuing. We can stop for snacks but you have to eat them before getting back in, or after we arrive. Taking ten-fifteen minutes to eat some fast food or store snacks isn't going to make us catastrophically late for anything. You're thirsty? Water is what you can drink.
I don't want food waste in my car. I don't want food odor in my car. I don't want sticky drinks spilling. I don't want greasy fingerprints on the dash or leather. My wife has come around and doesn't fight it, kids even learned.
My car, my rules. What are yours?