We're visiting family over the holidays and I would like to bring some bags of frozen breastmilk so my in-laws can feed DD2 if needed. I have a Medela ice pack and cooler bag but I don't know if that would actually keep frozen milk frozen. The flight is less than 3 hours but travel time adds up when you include driving to and from airport each way, security check, etc. How do you keep frozen milk frozen when flying? Or would just suggest pumping the day before and freezing it when I get there?