A few years ago my wife invested in a coupe of those 32 oz stainless steel insolated drink cups. Those things will keep a little ice and water cold all day in 90 degree heat. We carry an 18 can tall cooler in the trunk. in the cooler we carry pop, a 1/2 gallon of milk (my wife's addiction, she wants a glass of milk every night), a few bottles of water (we carry the flavored drink mix for 16.9 oz water bottles), and we put one of those stainless cups in the cooler. The other stainless cup we fill with water.

We start the morning off with a sit down breakfast, usually at a truck stop. We fill the gas than, get a bag of ice for the cooler and split the cup with the water in 1/2 and fill both cups with ice. One cup goes back into the cooler, the other in the cup holder in the car. My wife gets a large coffee (I don't drink the stuff, she has a special cup for that as well). I'll get aa Pepsi for the can koozie for the 2nd cup holder in the car.

We carry a bag of goodies behind the seat she can reach while we drive. In the bag is Twizlers in a zip lock bag, usually a couple bags of different nuts, a zip lock bag of cookies (my down fall), and Rice Krispy marshmallow squares, and a couple different bags of chips with the chip clips to seal them up and keep them fresh for a week.

We often stop someplace around noon. might get something light to eat, or may grab a snack from the goodie bag, take a rest room break, and get out and stretch for a few minutes. If we need to change out the water cup, that will happen then. We also stop somewhere around 3 and repeat.

We are well past the point of the marathon drives. We pretty much limit our driving day to 6 hours or 300 miles. I tend to get tired after that, especially if its hot outside. We have arrived at the point that the drive is as good as the destination. If we see something along the way that catches our interest, we will stop and check it out. By traveling like this, we find we arrive at our destination relaxed and not wore out from the drive. We enjoy the trip so much better.
We also try real hard to stay off the interstate highways as much as possible, that makes for a much more scenic drive. it takes a little longer to get where we are going, but its more fun. Being retired helps a bunch. Gene