When my youngest was on formula, I bought the ready to feed single serve nursette bottles. I brought 6 on the plane (I always travel with 24hrs worth of baby supplies). I had no problems getting through security with them. I also brought a small can of powdered formula and a couple of empty bottles, just in case.
I had additional nursette bottles shipped directly from Enfamil to my resort so I had enough for the week as well as the trip home. I liked the convenience of the nursette bottles since they do not need to be refrigerated.