to assemble, each person manning (attending to) his station, prepared for departure of an aircraft, ship, etc
to "be a man about it"; to do the things a good man is traditionally expected to do, such as: taking responsibility for the consequences of one's actions; displaying bravery or toughness in the face of adversity; providing for one's family, etc
Hey son, man up, ok? There will be time for tears later.
To form small teams, especially pairs, to reduce the likelihood of an individual suffering harm without being noticed or because of the nature of the task to be accomplished