Continuity mistake: When Ferris enters the cafe and announces they have a customer, he still has the stick in his right hand. He lays the stick on the counter as he begins to climb across. As the camera pans, and then back as he gets on the counter, a menu is now covering the stick.
Other mistake: When Ferris first arrives in the town the the church bell chimes seven times indicating it's 7 o'clock. Later the bells chime again but this time only four times indicating 4 o'clock. Surely he didn't walk around the empty town for 9 hours.