When Carter goes to clean out Greene's locker, the door swings open to the right. However, when Greene left the ER for good, his locker opened to the left.
The stethoscope that Carter takes out of Mark Greene's locker and switches with his own is the wrong model. Mark Greene used a cardiology stethoscope either a Littman Cardiology or an ADC 601. Carter used a Sprague-Rappaport, which is what he removed from Mark's locker.
After the letter that Dr.Greene has written is pinned to the board in the ER, Dr.Lewis pins the bottom half of the letter to the Board. In the ending scene, you see the letter floating in the wind from the open doors. The bottom half is not pinned down and the first page of the letter floats away into the hall because it is not pinned down.