Milk is a good source of nutrition and is commonly used with breakfast cereals and in cooking and baking, but presents some challenges onboard because it is best fresh and refrigeration is limited or absent. Fresh milk is rarely available after a week at sea because of the storage problems.
Its best replacement is UHT milk, which is treated with ultra high temperatures to kill bacteria and thus can be stored for months without refrigeration. It retains most of the flavor and consistency of fresh milk.
It is also useful to provision some evaporated milk, which has the advantage of having some water removed and thus reducing storage space. It can be be reconstituted for use or used whole in cooking for rich, creamy flavor and texture. Evaporated milk has about 1/3 the milk fat of cream so it is not as thick, but can still be used in its place in cooking. If you need to add thickness to a recipe because you use evaporated milk instead of cream, add 1-2 Tbs of corn starch or flour.
Powdered milk is also available that can be reconstituted with water.