8 hour drive and breast milk

Hello everyone! Hoping someone can help me. We're driving a little over 8 hours today to go back home from Chicago to Canada and I have 5 bottles of breast milk to use for the car ride. I have the ice pack that came with it to store it. I know it can be out in room temperature for 5 hours, but with the ice pack can. It be out longer? They're 4 oz each. Or if I put it in a cooler with ice would that work better? Any help would be great!!! Thanks!