If you can figure out a way to get liquid formula through security, I would suggest the Similac ready to feed bottles, and a pack of their ready to use nipples and rings
http://www.amazon.com/Similac-Advanc...+ready+to+feed

They are 60ml bottles so far more appropriate size for a 5 week old than the 250ml which you'll probably have a lot more wastage with. And the one time use nipples makes it a lot more convenient since all you do is screw the nipple on the bottle and feed. No messing with powdered formula and dirty bottles