I take steak, hot dogs, and frozen chili (the kind that comes in a plastic tube like pork sausage).  It all stays nice in my cold sack. Ever stepped out of a swimming pool on a 95 degree day and been hit by a tiny breeze that made you shiver? It's the same principle. I had my wife make me one. Basically a canvas bag with a terry-cloth lining. Plastic (so it wont rust) zipper sewn in the top. A couple of D-rings sewn to the corners and I can clip it onto the outside of a portage pack. I dip the bag in the lake to keep it wet. Doesnt need to be dripping wet, just wet.  It'll keep butter firm for the entire trip. Just keep it wet and lay it out of the sun. An old boy scout trick. I had my Canoeing merit badge sewn on the outside. It that sick or what?