J.D.
Hey R.,
I have not yet flwon with my little girl but have had quite a few friends fly with their babies (everywhere from an hour trip to Boston to a 9 hour trip to Hawaii). First, check out this link and print it out when you go: http://www.tsa.gov/travelers/airtravel/children/formula.shtm
It is from the TSA's webiste and it states that you are allowed to bring along formula etc, but quite often the screeners are not up to date, so bring the article with you.
Also, a friend of mine brought about ten pairs of ear plugs with her and handed them out to the passengers around her as a "nice gesture" saying I don't know what she will be like but just in case I wanted to pass these out. Sometimes that is all it takes because you are at least admitting that there may be a crying baby and not just bringing a baby on the plane.
Good luck with flying and I am sorry to hear about your relative.
~J.