Answer: A patched up American Flag that his son had carried throughout the war until he died.
Step-by-step explanation:
His son had died the day before, and while Benjamin mourns him and doubts about his commitment to the war, he founds the flag in his son´s saddlebags. When he shows up to the Battle of Cowpens, horseback with the flag up, Martin shows he has ultimately embraced his convictions and decided to use the flag to give impulse to the exhausted colonial army.