Big Bird wants to show the viewers something that is red, and he knows he has something red in his grocery bag, though he has trouble finding it. While he is searching for something red, several red things show up in the background. After giving up he sits on the other bag that he did not look for and the reader soon finds out Big Bird wanted to show them tomatoes.

Among the red objects that pass by Big Bird are Mr. Macintosh and his apple cart, parade floats featuring Little Red Riding Hood, a spoof on The Tournament of Roses Parade, Uncle Sam and Santa Claus. Big Bird speaks directly to the reader in word balloons, comic book-style. -- Muppet Wiki

Big Bird is trying to show us something red, but he can't find anything in his bag that is the right color. Meanwhile, behind him, fire trucks, painters, all kinds of red things and people are making an incredible mess. Big Bird is, of course, totally oblivious.

Just the kind of nonsense the little ones love. ( )