Yes you can... well, sort of. If you are traveling with a toddler, they will allow you to carry "a reasonable" amount of juice and/or milk. The reasonable amount thing is the kicker, it isn't specific. So you cant bring an entire case for a 1hr flight, etc. You have to declare that you have it and pull it out of the bag, you will be pulled aside by security and they do this weird swab test thing to it. Then you can go. We brought juice boxes (usually one or two) on flights from when my daughter was age 2-4. Now we pack a few koolaid powders and an empty water bottle and just fill it up after security.