Green eggs and ham
The eponymous green eggs and ham are a humorous addition to the story but are also symbolic. At first, the green eggs and ham look unappealing and repulsive- certainly not something you'd want to eat. However, once they are given a try they actually turn out to be delicious. As such, Seuss uses green eggs and ham to encourage his readers to give new things,
Sam
Sam is a force of enthusiasm and energy in this story and does not give up even when he is rejected. He is persistent in trying to get The Big Guy to try the green eggs and ham, making him a symbol of perseverance and persistence.
The Big Guy
The Big Guy refuses to try the green eggs and ham, despite the fact he is assured that they are delicious. As such, this character represents cynicism, distrust and inflexibility.
Allegory
This story is essentially an allegory for the importance of trying new things, even if they are unfamiliar or don't look appealing. This is represented by the green eggs and ham, a dish that Sam tries as he is an open and trusting person.