Yes, you can take milk on a plane, but the rules differ significantly based on whether the milk is for an infant or for personal use. If you are traveling with a child, breast milk, cow's milk, and baby formula are considered "medically necessary liquids" by the TSA and almost all international security agencies. This means they are exempt from the 3-1-1 rule; you can bring them in quantities larger than 3.4 ounces (100ml) in your carry-on bag. You must declare these items to the security officer for manual high-fidelity screening, which may involve opening the container or using a vapor test. If the milk is just for your own coffee or cereal and you are not traveling with a baby, it must follow the 3-1-1 rule (3.4 oz or less in a quart-sized bag). To avoid the hassle of liquid restrictions for personal use, many travelers buy milk in the terminal after passing through security. If you are bringing frozen milk, ensure the ice packs are completely frozen solid at the checkpoint, as slushy or melted ice packs may be confiscated.