I experienced the same thing with my firstborn. It was horrible, and I felt totally rejected by him at first, decided to try pumping, then had a problem with expressing my milk. I ended up giving him ready-to-serve bottles of formula that I had from signing up for freebies. He lapped them up. I was devastated, yet relieved.
Bless you for doing what you think is best for your precious baby. Surely you will be able to have an insulated cooler? My brother is a diabetic, and he carries his insulin in a soft-sided insulated cooler. He will be flying on Sunday.
I've thought about the insulated cooler. And if worse comes to worse, that is what we will do.
But there are also limits on how cold that will keep the milk and how long the milk will stay good at that temperature. My biggest fear is that milk that I'm traveling with will go bad and my daughter will be screaming in hunger as I try to pump to keep up with her demand. But heck, I have that fear when I have a refrigerator handy!