Jerry is eating a "black-and-white" cookie. In different angles of the shot, the colors of the cookie keep flipping from one side to the other, and the size of the bites out of it change inconsistently. 'The Seinfeld Coffee Table Book', released in the November 2007 complete series package, reveals that this was a goof.
First George suggests buying "Ring Dings" at the liquor store. Then when he and Kramer are in the liquor store, we see beer for sale. By law, liquor stores in New York State are allowed to sell liquor, wine and lottery tickets and nothing else, including beer.
The newsstand that George and Kramer visit has the magazine "Entertainment" with covers from five different issues spread out over the rack. A newsstand only carries the most current issue of a magazine.