It's really important to give your neck a good enough amount of cushioning and support to protect it from the bumps on the road. Too much shaking in the car can lead to lots of problems for different parts of the body and dehydration can be a major factor contributing to muscle cramps and stiffness, so drink plenty of water and other essential fluids throughout your drive.
Make sure to never sit on your wallet. Sitting on top of your heavy wallet or phone can create pressure on the lower part of your back and lead to a lot of pain. This is why neckrest pillows in cars are so important for travel.