As they get close to Agloe, Lacey and Quentin begin listing everything they know about Margo, from the make of her car to the color of her hair. Ben points out that they already know this information, but Quentin does not care. He wants to remember Margo now, while he is still hopeful that he will see her again.
Quentin knows his ideas about Margo may soon dissolve, and talking through his memories and perceptions of her is a way of reconciling himself to that possibility rather than denying it. He is preparing himself to accept whatever he finds in Agloe, regardless of whether it is what he hopes to find.