Continuity mistake: When Walter steps into the cat poo he gets it right under the middle of the shoe. When he then lifts his foot to take a look it's stuck under the front of the shoe with no sign of poo in the middle.
Continuity mistake: When the woman almost overturns the shelves when Wes is signing his book, you can see that in the first shot, all the upstanding books are falling down. In the next shot some are upright, and then in the next they are all lying down again.
Continuity mistake: Claire sits on a blanket and empties a bag of stuff on it. Then it seems empty when she takes it from the ground to hand it over to Henry. The stuff would have sounded and the blanket is to light when she takes it from the ground to hand it over to Henry.