I agree with the pre-filled bottles. Also I found that sending more bottles with less in them worked the best. We started with 4-5 3oz bottles a day and I gave them a bag of frozen to keep in the freezer just in case.
Unfortunatley when I froze it I had it full - ie 5 oz! They did thaw it and use it, but she only drank 2 oz AND THEY DUMPED THE REST !!! I wanted to
Now at 6 months, we are up to 3 5oz bottles a day (and they had a bag of 3oz in the freezer, as a "snack" just in case). I also just started to send her with a bit of solids to munch on for fun during the day.
I will say that my only issue with them has been that they didn't get that BF babies didn't need as much as FF babies. They kept insisting I send more milk! We finally got over that, but it took months! DD is the only BF baby in the room. Now that I am sending solids and labeling them "for fun" (not breakfast, lunch, etc) they again got very confused.
They seem to think their job is to get everything I send into DD!