It is said with great truth, that an army travels on its stomach. The point is that logistics are a critical contributor to success in addition to training, courage, weaponry, etc. Or, in this case, maps.
Although the fighting had moved inland, sporadic artillery shelling and intermittent sniper fire from Germans still holding their positions on the bluff hampered movement on the beach. Henderson's job was to distribute maps (a critical and never-ending process -- eventually in the Normandy campaign, the U.S. First Army passed out 125 million maps), but because the front line was just over the bluff at Omaha, only men, ammunition, weapons, and gasoline were being brought ashore, so he had no maps to hand out. He and his section unloaded jerry cans of gasoline, the first of millions of such cans that would cross that beach.