When Sam and Eric come racing down from the mountain, terrified at having seen what they thought was the beast, Jack responds with what could certainly be considered bravery. While others are asking questions and delaying, he says "This’ll be a real hunt! Who’ll come?” Though it may be detrimental to the boys in the long run, this immediate reaction to fight back against their fear and this thing they think is a beast demonstrates a type of courage on his part.
Once they discuss where the beast might be and decide to go down to the castle rock part of the island where they think the beast might live. When they get there, they hesitate but Ralph steps up. Golding writes:
"Something deep in Ralph spoke for him. 'I’m chief. I’ll go. Don’t argue.'"
Ralph had long before accepted the responsibility of being chief but here he demonstrates the willingness to also be a leader when others were frightened.
As Ralph goes out to the narrow neck of rock connecting the outcropping to the island, Golding writes that "he forced his feet to move until they had carried him out onto the neck of land." This ability to overcome the fear that would keep him immobile is important in demonstrating Ralph's courage.