Oh yes indeed, you should always have your bun in a carrier if she’s being driven around in your car because it’s not safe to have them running around free in the vehicle; carriers for small dogs or cats are suitable for rabbits, and a lot of people use them. In fact I’ve been shopping for one myself the last few weeks and think I’ve finally found the right one (see my thread on the subject in Habitats and Toys). I suggest you pad the carrier’s inside with a blanket or some such for comfort for your bun and to help cushion her in case you have to brake suddenly. Be sure to belt the carrier in securely and hook it up much as you’d hook up a child seat. Hay and water are good ideas too – I should remember to get a small water bottle myself for the carrier! I’ve seen some people give their rabbits greens to munch on while they’re in the carrier too. Also, if it’s hot in your area that day, remember to run the A/C while they’re in the car, and you may want to shade the carrier (be careful not to block the air vents) so it’s protected from excessive direct sunlight.