For many people, the dog is a member of the family. Our schnauzer Heidi (now in doggy heaven) was like that to us.
When soccer Saturday rolled around, she was bundled into the minivan along with the duffel bags of sports stuff.
At the time, I didn't go for the doggy car seat, but today I've warmed to them. They're a good idea if your dog tends to roam or jump around visiting the rest of the family members, seat by seat.
Yes, I know cats travel, too. But dogs are the more frequent travelers. I've yet to see a family let Fluffy the cat bound out of the hatchback at soccer practice or baseball game. If you do take a cat in the car, I would advise putting her in a carrier. Cats will slink under the brake pedal without your realizing it - until you can't press the brake pedal.
If you want to confine your cat or dog on a somewhat regular basis, invest in a gate for the back of the minivan or car. Pet car essentials include:
Your pet car survival kit should include a leash for each pet.
This may seem like a "duh," but often dashing out the door, you or the kids might forget it in a rush.
By having a "spare" or second leash already in the car, there's less to think about in a rush to get out the door to soccer practice.
Sometimes, your errands or carpool might take longer than expected; be prepared, so your hungry animal doesn't get restless or loud (barking comes to mind here).
If you're unsure whether there will be a faucet or hose nearby your destination(s), consider including a water bottle in your car kit.
They needn't be fancy - even a plastic picnic-style dish will do. In a pinch, it's nice to know you don't have to consider whether your destination(s) will have pet-friendly feeding or watering areas.