The contrast represented in this extract is, firstly, between civilization and primitiveness. Ralph's recollection is about a place where there was comfort and food was in abundance, a place where he could read whatever he chose and eat whatever he wanted to. It was a place of family, since his mother had still been with them. In the place that he was visualizing, one could spend time enjoying little pleasures such as seeing wild ponies and enjoying the snow. He could indulge in his favorite pastime, reading, and choose to read what he wanted. Life, therefore, was civilized, as he expressed in his sentiment:
Everything was all right; everything was good-humored and friendly.
Life on the island was the opposite. Ralph had, earlier in the chapter, assessed their situation and done some introspection. He felt dirty and wished he could wash his shirt and that there was some soap. His hair was dirty and he wanted to cut it. He longed for a bath and when he looked at the other boys, he could easily see how filthy they were. He wanted to brush his teeth. His nails had been bitten to the quick, indicating the anxiety he had been going through. He and the other boys had become primitive. The rules of civilized conduct had been foregone. Ralph realized, with some disdain, that he had come to accept these conditions and that they had become normal to him.
In addition, the island involved a continuous struggle. The place in his daydream (home), did not demand much of him and he had so many choices. Here, choice was limited. They had to survive on what was available. They had to continuously find food--it was not readily set before them. Their survival depended on having shelters and making a signal fire for rescue, and it was compulsory for them to do so. At home, Ralph could choose which books he wanted to read and what activities he wanted to perform. Here, he and the other boys had to do what was necessary to survive.
Ralph's reverie accentuates the irony in the fact that the boys believed that they had greater freedom on the island when they had actually acquired more responsibilities than they would have had at home. This is a fact recognized by both Ralph and Piggy and largely ignored by Jack and his hunters. This contrast in perception is the source of the conflict between the boys and is what leads to the eventual chaos that transpires when Jack and his tribe succumb to their innate savagery.
The contrast here is between the idealism of Ralph's dream, & its reflection of the lost society from which the boys came, & the reality of their lives on the island. Ralph's dream is of a cottage in which his family once lived, where wild ponies would visit at their walls. He remembers:
When you went to bed there was a bowl of cornflakes with sugar and cream. And the books-they stood on the shelf by the bed, leaning together with always two or three laid flat on top because he had not bothered to put them back properly...Everything was all right; everything was good-humored and friendly.
These recollections of the peaceful, contented life he had lived before the island swarm up before he is unable to stop them. They are also destroyed by the appearance of a wild boar, which Ralph attempts to kill. This moment of the novel reveals Ralph's weakness-his easygoing attitude and inability to see the evil in others. Instead, he dreams of peace without making the effort to establish it on the island.