They came out of towns from the western side of the Sea of Galilee. Word spread as they watched the boat leave and as it traveled. They outran the boat. Some say that everyone brought his own lunch. The early church exaggerated it or minimized it.
Liberal commentaries explain it away.
Rest and Relaxation. Avoid doing things in your own strength, but don't just sit around waiting for God to do it all. The disciples did what they could - they got the lunch and brought it to Jesus, they organized the crowd and distributed the food, then they gathered what was left over. But they let the Lord do the miracle. Both the little boy and the disciples ended up with more, and so did the crowd.