In F. Scott Fitzgerald's The Great Gatsby, one memorable thing Gatsby sees of significance is a green light on Daisy's dock. At the end of Chapter 1, Nick the narrator describes how one night he saw Gatsby out on his own dock. Nick had just been about to call out a neighborly hello to Gatsby when he saw Gatsby do something unusual:
He stretched out his arms toward the dark water in a curious way, and, far as I was from him, I could have sworn he was trembling. (p. 19)
When Nick looks out towards the water, all he sees is a "single green light" (p. 19). Later, in Chapter 5, we learn that the green light is actually at the end of Daisy's dock. We learn this when Nick observes Gatsby confirming to Daisy that "you always have a green light that burns all night at the end of your dock" (p. 72). Hence, what Nick observes Gatsby doing at the end of Chapter 1 is reach out trembling arms towards Daisy's dock across the water as if he can pull her towards him. The light at the end of her dock becomes significant to Gatsby because for a while it's the only thing of hers he can see.
A second thing Gatsby sees in his life that proves to be meaningful to him is the sight of Dan Cody's yacht as Dan drops anchor in Lake Superior. Nick flashes back to this part of the narrative in Chapter 6. At the age of 17, Gatsby, whose legal name we find out is James Gatz, happened to be "loafing along the beach" of Lake Superior when Cody dropped anchor. At the sight of Cody's yacht, young Gatsby decided to borrow a rowboat and row out to the yacht to see if he could meet Cody. Cody was an extremely wealthy man due to owning silver mines in Yukon, and when he met Gatsby and saw how ambitious he was, Cody invited Gatsby aboard and took him to the West Indies. Cody served as Gatsby's mentor, which eventually led to Gatsby creating his own wealth.