N.,
I posted this to Lindsey's question as well, but I modified to respond to some of the others with "helpful" advice.
I took my Medela briefcase looking ELECTRIC pump on the plane with me. I had no problem going through security with it. They seemed to have been trained on what it was, and only asked a couple of questions, but didn't really make me open it. My bag has a place for ice packs, but I really don't remember if I kept it or not. On another trip, I had taken my breastmilk bags through security, no problem.
I did pump in-flight in the lavatory, and I must say that it started out awkward, b/c I was trying to be discreet (more commonly read embarrassed), and find a time that there wasn't a line waiting. I finally couldn't wait any longer, b/c I had already waited too long. I got situated, and was fretting about taking so long, and the noise it was making, but kept reminding myself this was for my baby. Then, to top it all off, I must not have latched the lock very well, b/c the door moved inward, and a guy was trying to get in. I think he was more shocked than I was. Of course, now I was very uncomfortable, trying to finish up with one foot propped keeping the door closed, trying to stay balanced on those little plastics seats, and trying to keep my pumps attached, all the while thinking no one but my husband has had that view before.
I look back at it now, and see it as another funny tale for the wanna-be big-time traveling executive, but in the end still just the small-town farm girl. I'm laughing now, but even to this day, I don't think I've even told my husband the story.
Best of luck to you, N.!
J.