Two of the names on the wall behind Dr. Kelso while he's talking to Boon are Jojo Wilson and Sparky Redoglia. Jojo and Sparky were the names of the two dogs that Kelso was telling Boon about.
The song JD and Turk are air banding is the show's opening theme "Superman".
When Kelso sits on a bench outside claiming he still sees the faces of all the patients he lost the camera cuts to the reverse angle on the hospital. In the top center window you can see what appears to be the hospital's employees/the rest of the cast in that window.
The two dogs Dr. Kelso told the story about were JoJo and Spike, according to the closed captioning.
The song playing while dr Kelso is saying thank you and his goodbyes is "Little Victories" by Matt Nathanson.