Any liquids you bring have to be smaller than 3oz and you can only bring as many 3oz packs as will fit in a quart size ziplock bag. EACH person with a ticket can have one quart size bag full of 3oz or less liquid/gel items. If you have an infant you are also allowed a small amount of sealed baby food and formula, but check the TSA website as the rules on doing this are complex and I have personally seen mom's arguing off to the side at security, so I think they are quite strict.
One way we got around the "can't bring juice boxes" and yet still not have to pay the outrageous prices of the shops beyond security......bring EMPTY water bottles (or sippee cups if your kids are that young).....fill them after security at the water fountains or in the restrooms. Bring along those flavor packets to make your drink. We use the Crystal Light copycats from
Walmart, but I believe that Koolaid makes a line of them if your kids don't like the others. I found the Walmart brand "fruit punch" to be too sweet for my adult tastes, but the kids say it's just like koolaid.
Like the other poster said, food has to be non-liquid or gel (or less than 3oz), so pudding/jello is out. We brought along our homemade version of Lunchables......cheese slices, crackers, deli meats (salami, bologna, etc) pretzels, grapes (we froze them so they're not only a fun snack but they kept the cheese/salami cool until lunch time as you can't bring along Blue Ice). You can purchase peanut butter and jelly in 3 oz packets (see minimus.biz) and bring your own bread for sandwiches, but I've read of people not being allowed to use PB on board when someone has an allergy....so it wasn't worth the risk of not being able to eat it since we liked other foods. For what it's worth, I've NEVER been on a plane that announced you couldn't eat PB, but again, not worth the risk because then what do you do, you can't even run and get something expensive because you're already belted in!
By the way...if you bring your lunch items in a "disposable container" (we used a grocery sack) then it does NOT count towards your carry on allowance. If you bring it in something permanent, like a lunch box or collapsible cooler it is considered a carry on.