In my experience- the powered milk by itself wasn't a big hit- but if you mix it with something else, it goes over better. I posted somewhere else about including instant pudding mix with the dried milk, and that seemed to go over well. My contacts were much happier when I sent Parmalot (a vacuum packed liquid milk that comes in juice box type containers.) It is heavier than dried milk (but not as heavy as canned evaporated milk lol) but doesn't need refrigeration, etc so it is a good alternative.
Everyone I've sent to seems to love the oatmeal packets (as well as granola bars, power bars, etc). Just in case anyone is from the south- I also throw in grits (ususally the mixed variety) and even boxes of cereal (plus sandwich size ziploc bags.) I'll also throw in a few bags/boxes of craisens, raisins, dried dates, dried coconut, nuts etc that can be added to the oatmeal for some variety/ ( I try to buy 3 or 4 boxes of different oatmeal flavors. I then open the boxes, put the individual packets in gallon size ziploc bags and they fit very nicely in a box. I had one contact (a sniper) ask if I wanted to come to visit him in Afghanistan and pack his backpack for him as he could never figure out how I could get so much stuff crammed into one box, and he wished he was as efficient with his pack.)
My DD is a long distance runner and she eats oatmeal almost every morning (all year long) because it is such a great source of carbs, proteins, etc- and it sticks with you. I guess that is one reason why it is so popular.
Sandi