1) Get a good map. CAA one is good. If you lost find a gas station buy a map as soon as possible. The map is expensive there, but gas also expensive. There are visitor information center at state border. They may have free map and motel list. Stay in motel at small town near big city they usually have good price.
2) Take good rest. Don't drive over 10 hour per day. Take a nap after lunch.
3) Drink only water. in long drive other things may upset you. Bring a cooler. You don’t need ice. In this weather leave the cooler in car overnight, you will have cool water all day.
4) Start to look for gas station when it is half full. Because you don’t know how far is next gas station?
5) Check engine oil at every gas fill. Especially for a old car. Because in long distance highway driving, you may lost 1L oil every 1k. I find add 10w 40 or 15w-50 oil will reduce the oil consume.
6) Top up all fluid before the trip. Engine, transmission, brake, power steer, coolant.
7) Follow major highway,