Buy or borrow a two ounce Tupperware "tup". Fill with Milk, put a
string in the milk before you put on the lid. Lower the container
into a pint sized widemouth Thermos jug half full of ice. add a bit
more ice,lead string out of jug before putting on the lid. Take to
work. milk stays cold at least half a day, and you only have two
ounces so none is wasted.