traveling with breast milk!

Jessica
Hello! I'm hoping some of you experienced pumpers can help me out 😊
I'm 2 months pp and EBF. I just started pumping a week ago to start a small stash for dad or emergencies (I'm a SAHM). Right now I'm only pumping once a day, and I'm getting 2 1/2 - 3 1/2oz or so. I'm usually full in the morning so I just feed her on one breast and pump the other. So I don't get much each day, which I'm honestly okay with! Except...
We're traveling by car 4 1/2-5 hours for the holiday, and the next day we're taking our 3 year old to see a dinosaur exhibit and my mom is watching our 2 month old.. So I'll need to leave at LEAST 2 bottles for her, preferably 3.  What's the best way to travel this distance with breast milk and keep it frozen? I won't be able to pump enough between the time we get there and when we leave baby with her.. Â