The car is the most practical way to travel with a Californian. A secure, well-ventilated carrier keeps the rabbit from moving around the vehicle and protects it during sudden stops, and it should be roomy enough for a sizeable rabbit to turn around comfortably.
Heat is the primary hazard. Rabbits handle heat poorly, and a parked car can become deadly within minutes, so a Californian should never be left in a stationary vehicle. Traveling during cooler hours and keeping the cabin air-conditioned in warm weather are essential precautions.
Bringing familiar bedding, the rabbit's usual hay, and water helps limit stress on longer trips. Since anxiety can disrupt a rabbit's sensitive digestion, keeping intake steady and minimizing handling at stops supports gut health on the road.