Be sure to transport it in your trunk and not in the passenger compartment of your car!!! If you have a hatchback keep a window cracked, the fan on and air recirculation off so that air circulates in the car. Keeping it in a cooler is a good idea as this slows down the rate at which the CO2 gas is generated as the dry ice sublimates and makes your dry ice last longer.
CO2 is not poisonous, but it is heaver than air and will displace air. It can cause you to suffocate or black out in an enclosed space with no air circulation.