Ralph, early in the novel, makes more of a concession to the idea of enjoying the paradisical island than he is to do later on:
“Now we come to the most important thing. I’ve been thinking. I was thinking while we were climbing the mountain.” He flashed a conspiratorial grin at the other two. “And on the beach just now. This is what I thought. We want to have fun. And we want to be rescued.”
The passionate noise of agreement from the assembly...
Ralph knows, right from the start, that the key priority really has to be making a signal fire in order that a ship can see them to get rescued. It's interesting that 'fire' becomes central to the island: and symbolic of both good and bad qualities. Fire for Ralph is about a signal fire - about rescue. And, for Jack, fire is about cooking the pig meat he has caught.
But what Ralph says here, in this second chapter, is what he goes on to believe more firmly later on:
“There’s another thing. We can help them to find us. If a ship comes near the island they may not notice us. So we must make smoke on top of the mountain. We must make a fire.”
Fire. Signal. Smoke. That is Ralph's priority.