Pets and cars often don't mix, and in some states it's even illegal to drive with your pets unrestrained. As such, it's important to make sure that your pets are either crated or seat belted in (in pet-friendly seat belts that you can buy at pet supply stores). This helps keep your pets safe and sound, and allows you to drive in the car without being distracted.
Don't let your pet drive with you in your lap. Also, don't leave them unrestrained in the back of your pickup if you are traveling long distances. Check with your state to see the state laws regarding pets and traveling- every state has different laws regarding pets in cars.