In the first level, go to the northernmost island, with the "HELP" sign on the beach that Decay found. Stand on the campfire near the wreckage with the "HELP" sign facing southeast. While facing southeast, walk up the hill and into the shade. Continue walking until you reach the top of the hill. Then, face northeast and walk through the brush to find an area where the sun is shining brightly. Look at that location to find Wilson, the volleyball from Castaway.