Complex sentence: He rented a large truck and filled with food, water and medical supplies and drove for four days to the earthquake site where he proceeded to conduct first-hand relief work supplying food, water and medical attention to people in need.
Split into simpler sentences: He rented a large truck and filled it with food, water and medical supplies. He then traveled to the site and conducted first-hand relief work supplying food, water and medical attention to people in need.