We had this dilema earlier this year. For the plane I bought a six pack of the pre-mixed (not concentrate) formula. The TSA pulled our bag aside and asked how much of it we actually needed. I said all of it, and he let us keep it. I also had jarred baby food and he also asked how much we'd actually need, and I told him what we'd use if we weren't delayed, and he said oh, you won't be and took the rest. Eh, like someone else said it depends on what TSA person you have and their mood at the time.quote]
Too late for you now, but do not tolerate this. TSA does NOT fly planes; they have NO IDEA whether or not you may be delayed, and they have no business second-guessing how much food your child needs to eat in a given period. Any time I get that song and dance I ask to speak to a supervisor, and I ask that supervisor to give me his ID information and to personally guarantee that I will not be delayed either in the airport or on the ground. Of course, the supervisor can't do that, so I get by with my supplies. I'm scrupulously polite, and it has never failed yet.
ALWAYS carry 24 hours worth of any special supplies that your child needs on your person, not in checked baggage. Do not trust the airline to provide it. Do not trust the airport to have anything except bottled water available; if there is a ground stop they will begin to run out of food very quickly. All but the very largest international airports don't normally have baby food, formula or diapers available for purchase in the first place, and even when they do the selection is very limited. You need to cover all the possibilities yourself.
I've been stranded on a runway for hours with a baby; it is NOT pretty. I've also been in situations where our flight was scheduled to depart at 4 pm but didn't leave the ground until 1 am; that's not helpful, either. Not having the proper supplies in hand would have transformed it into the seventh circle of hell.