Eric tells Hyde that if he were to move to New York, they wouldn't be able to do "serious damage to this town". He mentions that they wouldn't be able to paint a "pot leaf on the water tower", which is what they had already done in the previous episode, "Water Tower".
At The Hub, before the opening credits, the candy boxes on the counter shift positions during Hyde's conversation with the Punk Chick. A small bag of chips also appears in the Abba-Zabba box.
In the first scene after the opening credits, Kelso is playing Pong with Eric. Next to Kelso, in front of the telephone, is a modern plastic water bottle.
Hyde pictures Chrissy standing with two guitars (Stratocasters) strapped around her. The guitars have locking tremolos indicated by the bolts on the back of the neck. The episode takes place in '77, but locking tremolos weren't invented until around '79. The Stratocasters also have the original headstock design. During '77, Fender was owned by CBS and featured the larger "CBS design" headstock.
The jar of Skippy peanut butter that the guys are eating out of is a modern plastic jar with a mostly blue label. The label design in the '70s was mostly white, with a blue border.