I have been exclusively pumping since DD was about a week old and my supply has been enough so far. However, she is starting to eat more and we are taking a vacation later this summer and since I can't really take freezer stash with me, I want to have a back-up plan. So- what formula do you use? Can you mix formula with breastmilk? if you have a simiar situation did DC have a hard time with addition of formula? Any help is much appreciated.