The hold *is* the same pressure as the cabin, but that does not mean the container will not experience a pressure change -- because the cabin's pressure changes during the flight. Just as you notice a soda bottle will change shape/pressure as the plane ascends, so will the tupperware.


I wouldn't use a tupperware -- that is not anywhere close to leak proof. And there is no way to guarantee what direction your bag's "up" will be after loading, and you will likely end up with a soggy bag.

Actually, you might try using a plastic screw top soda bottle to hold the liquid. That is designed to withstand >100psi. Screw tightly closed, and then put that in a plastic bag for safety. You could even freeze it beforehand to provide some cold, if you're worried about that -- but if it came in a cardboard container, I'm guessing refrigeration is not required.

Also keep in mind a big bottle of liquid might cause your bag to be searched, so make it easy for them to do so.