There are two things that both Ponyboy and Johnny like which are symbolically important: sunsets and Robert Frost's poem, 'Nothing Gold Can Stay.' It is Ponyboy who imparts an admiration of those to Johnny. Their appreciation of such things shows how both Ponyboy and Johnny have a softer, sensitive side which is not really apparent in most of the other Greasers. Ponyboy is particularly artistic and given to daydreaming; as the previous answer states, he also has an interest in writing and of course the whole story is his narrative.
The poem, 'Nothing Gold Can Stay' comes to have a profound meaning for Johnny. Despite being not so artistic and literate as Ponyboy, he seems to have a greater understanding of it and he refers to it on his deathbed when he urges Ponyboy to 'stay gold'. Johnny recognizes that the 'gold' of the poem represents purity, innocence, beauty, joy, all the good things of life and human nature which, sadly, are often all too soon stripped away by the harsh realities of the world. Johnny has seen and suffered a lot of violence and neglect in his life yet he never became hardened and uncaring like so many others, and he exhorts Ponyboy to also retain the 'gold', the goodness in his nature, no matter what happens.
The sunset also functions as an important point of connection, when Cherry, the Soc girl, remarks that she can see it just as well from her part of town as Ponyboy can from his. Here, the sunset is seen to link the Socs and Greasers who on the face of it are diametrically opposed to one another. However, Ponyboy comes to understand that underneath their different exteriors, Socs and Greasers, both being human, are really the same.
JOHNNY CADE. Johnny is poorer than the other boys and seems to have very few possessions. He is proud of his hair, like the other boys, and he treasures his switchblade, which he carries primarily to protect himself from the Socs. His paperback copy of Gone With the Wind, given to him by Pony, becomes important to him. He practically idolizes Dallas Winston and considers their friendship invaluable. And he values the park as a haven when his parents are fighting.
PONYBOY CURTIS. Like all of the boys, Pony is proud of his hair and blue jeans--symbols of all the greasers. Pony likes his cigarettes, but he also realizes that they hinder his skills as a runner (he is on the school track team). He especially values his relationship with brother Sodapop. He also recognizes his writing skills, but he doesn't seem to value them until the end of the novel.