
Milk at the bar almost always means cow's milk, used for creamy body in nogs, flips and shakes.
It gives a drink opaque, creamy body without the weight of cream. A small measure softens a drink; a large one turns it into a shake. Its other use is the opposite: in a clarified milk punch, acid is added so the milk curdles on purpose. Straining out the curds removes color and harshness and leaves the drink clear and silky. In a shaken drink, add it last and shake briefly.
Other cow's milk
Works one for one. Reduced-fat gives a slightly thinner drink, and skim a noticeably thinner one than whole milk.
Evaporated milk
Diluted with an equal amount of water, it comes close to whole milk in fat and sugar, though it tastes faintly cooked.
Oat or soy milk
Use in the same amount in drinks without citrus, though their own flavor shows through.
Cream
Even half-and-half has over three times the fat of whole milk. It gives a much heavier drink.
Will not work as a straight swap. It is more than half sugar, so cut back on any other sugar.
Keep it in the fridge, by the date, away from anything strong-smelling. Milk left out on the station warms faster than you expect, and warm milk curdles with citrus where cold milk would hold.
Non alcoholic