In the very beginning of the episode when Walt is going through the glove box in the stolen car a cassette tape falls out and he puts it on. The song is called El Paso by Marty Robbins, about a gunslinger who falls in love with a girl named Felina, and at the end the gunslinger is in a gun fight and shot. A lot of the lyrics kind of lay out what happens through out the episode, but when he's driving away: "I saddled up and away I did go, Riding alone in the dark. Maybe tomorrow A bullet may find me. Tonight nothing's worse than this Pain in my heart." Vince Gilligan also said he modeled the ending after The Searchers, which makes is that much more fantastic for me. Others say Scarface (which I guess Gilligan already made a comment about really liking the end of) but I feel like The Searchers really covers the Jesse/Walt relationship at the very end. So much fantastic stuff in such a simple ending. The flash back of Jesse carving the box, Walt perfectly channeling Mike with the line "If that's the way we're going to do it Elliott you're going to need a bigger knife." The throw back to Saul's laser suggestion. Someone on The AV Club said Felina was basically an epilogue to Ozymandias and I definitely agree and thought it was perfect.