The Grass is Always Greener - S3-E12
Continuity mistake: Early in the episode when Cory is talking to Shawn by their lockers, Shawn closes his locker and you can see one of the straps from his backpack sticking out on the bottom-right side of the locker. A few shots later, the strap is now sticking out on the bottom-left side. About a minute later in the scene, just before Topanga comes to talk to Cory, you can see the strap is now sticking out of the bottom-middle area.
Chosen answer: In the present day, with the United States abiding by more stricter school health laws, for the most part this wouldn't be in school cafeterias as many cannot even have carbonated beverage machines now. However, in the 90s when the show takes place, it wasn't unheard of for there to be coffee machines in the cafeteria of small schools where the teachers eat with the students as we see them do often in the show. The idea being that the cafeteria was small enough so a teacher or hall monitor could catch a student before they could drink the coffee.