“Mug ups" were an important part of life for fishermen. They would gather and have a hearty meal and warm up whenever they could take a break. Today, this nautical expression still describes a gathering of people for a drink and meal
Today, Mug-up is used by Scouts Canada to describe an evening snack (after dinner, but before Campfire). It is usually soup or hot chocolate and something to munch on (grilled cheese, etc).