How to keep breast milk frozen during my flight?

Tanya
Hi ladies,
Next week I'm traveling outside USA with my husband and 6 months old baby. I've never travel with a baby before since he's my first. I am wondering if I can bring some frozen milk with me as a backup. How can I pack this up? Can I bring it on my carry on?  How much is allowed to bring on the plane)
If anyone has experiences with this please let me know.
Thank you!!!