The Winchesters meet Adam at Cousin Oliver's restaurant. This is a reference to the character "Cousin Oliver" in The Brady Bunch (1969). Cousin Oliver was brought in during the final season of the show in an attempt to recapture the cuteness of a young child, as all the original cast had gotten much older. Many fans consider this to be when The Brady Bunch (1969) itself "jumped the shark." (In actuality, NBC's Sanford and Son (1972) was what killed the Bradys).
The expression "jump the shark" is a term commonly used to describe the point in which a TV show has clearly passed its peak, often by adding characters or having bizarre plot points. The term originated from a Happy Days (1974) episode (Hollywood: Part 3 (1977); in which Arthur "The Fonz" Fonzarelli performs a stunt in which he literally jumps over a shark while water-skiing. When Sam and Dean enter the diner, a poster for the "Fonzarelli Water-Skiing Championship" can be seen on the wall.
When Dean and Sam determine who is going to go down the floor vent, they play "Rock, Paper, Scissors". Dean always throws scissors and Sam knows this and always throws rock.
A display card in the boys hotel room when Adam comes to see them, advertises happy hour at the Sonny Buono lounge and features a pic of a mustached Kim Manners. Kim was a much loved producer and director from the show, who died in Jan 2009 and was mentioned in memorial, post credits, in the episode Death Takes a Holiday (2009).
Dean identifies himself as Agent Nugent, after hard rock's Motor City Madman Ted Nugent.