choose a different chocolate or purchase no chocolate at all. However, once the girl he wants to date wants the chocolate, he will not rest until she’s satisfied. This speaks to how being in love will make people act in irrational ways to please the person they love. It also shows how he is willing to sacrifice something of his own (the orange) to make the girl happy.

It could be that the rite of passage referred to in the poem is simply the rite of courtship, of making the girl for whom the narrator pines "his girl." He goes through all the courtship rituals: picking her up from her home, touching her shoulder, and taking her somewhere he knows she will enjoy (a drugstore with an apparently satisfying candy selection). His choice makes her smile with a "light in her eyes," and he asks her what she'd like. Then, when he finds that she wants something he cannot quite afford, he does his best to get it for her; he so wants to please her. The fact that the lady at the counter holds his gaze, "knowing / Very well what it was all / About" seems further evidence that this courtship is the main rite of passage discussed in the poem. It is a story told again and again— boy meets girl, boy loves girl, boy gets girl—and this is why the drugstore lady can be counted on to understand.  

Finally, in the end, they hold hands—their courtship cemented—and he calls her "his girl." She eats her chocolate and he eats his orange, and something magical happens: he seems to be "making a fire in [his] hands" as he peels the orange in the midst of the gray December air. This intense description is a clue to the intensity of the boy's feelings for "his girl": it may be an old story, told over and over, a rite of passage no less, but that makes it no less lovely, new, and bright to those who feel it for the first time.

"Oranges" is an interesting poem because it details not one but two rites of passage, the second of which is less perceptible but far more profound than the first.

The first, and most obvious, concerns male-female relationships. The poet tells us that this is the his beginning attempt to court a member of the opposite sex:

The first time I walked
With a girl, I was twelve,
Cold, and weighted down
With two oranges in my jacket.

As such, given the importance of love, marriage, and building a family of one's own, it is an obvious passage to a more mature state, all the more so in that the poet is successful in overcoming difficulties in pleasing the object of his affections.

It is in trying to give his companion what she wants that the poet goes through the second, and perhaps even more significant, rite of passage. It turns out that he has not brought enough money to purchase the candy that she has chosen. Instead of admitting failure, though, the poet makes an unspoken appeal to the human sympathy of the store clerk to assist him in this dilemma:

I took the nickle from
My pocket, then an orange,
And set them quietly on
The counter. When I looked up,
The lady's eyes met mine,
And held them, knowing
Very well what it was all
About.

The second rite of passage involves self-confidence and trust -- the confidence to make such an appeal, and the trust that the clerk will sympathize with him as a fellow human being who has, presumably, also felt love and overcome obstacles in its pursuit. The importance of this is underlined by the symbolism of the brillliantly colored oranges -- one exchanged for the candy by the grace of the clerk, the other remaining with the poet to be eaten at the same time as the purchased chocolate, at the conclusion of the poem:

I peeled my orange
That was so bright against
The gray of December
That, from some distance,
Someone might have thought
I was making a fire in my hands.

In trying to tackle this topic, I think we have to assume the type of perspective that can be seen in most reveries.  Obviously, the setting of the speaker being 12 years old gives us some indication of where we are and where we are being taken.  Adolescence, first exposures to independence, the advancement of experience supplanting innocence, and/ or dating.  These can all be extrapolated to being considered rites of passage.  Gary Soto is an author who emphasizes how our adolescence bears much "fruit" in who we are as adults.  The reason being is that we undergo experiences, or rites of passages, that leave indelible marks on our psyche.  Certainly, examining the poem and finding the lines to any of the concepts listed above could constitute as a rite of passage in this poem.

The theme is commonly understood as "the main idea of a poem or story." This one is a bit complex because it's commonly understood that these main ideas can usually be expressed in one word. The poem is powerfully about two things: (1) first love/date and (2) nostalgia. The two see equal in power to me, even complementary. 

Consider: Throughout the poem, two kinds of "opposites" are compared:

1. The colorlessness and cold of the surroundings with the color and warmth of the occasion. The narrator emphasizes the frost, the cold, the fog, and "the gray of December" and contrasts that with how the "Porch light burned yellow," how his girl's face was "bright / With rouge," and his orange, which was so bright that "Someone might have thought / [he] was making a fire in [his] hands." Note, in addition, that the colors he chooses--red, yellow, orange--are considered warm colors, something he emphasizes with his last line. The implication is that the occasion and his "girl" brought color and warmth to his cold and dreary world. 
2. The old with the new. When he takes her to the store, he leads her "across / A used car lot and a line / Of newly planted trees," where we pass the old and used and then a line of young trees, about to grow up. The adulthood and compassion of the saleslady is inherently contrasted with the youth and hope of the children (note, however, that the narrator does not hint at anxiety; he already seems mature in how he deals with the situation, not panicking or complaining when his "girl" chooses a chocolate he cannot afford; instead, he pays for it with a nickle and an orange, which is clearly not a prearranged deal, but his gamble works). Even in his memory, the "Fog [was] hanging like old / Coats between the trees," an image from the memory of a much older man. 

In addition, he returns to the idea of the transience of life and experience, which also emphasizes the theme of nostalgia. He begins the poem with "The first time I walked with a girl," suggesting that there have been many times and many years in the interim. As he walks to her house, his breath is "Before [him], then gone," like life itself. 

The brightness of the orange against "The gray of December" emphasizes how special this memory is to the older man, who has by now known love (and perhaps lost love) more than once by this point. This idea contributes to the theme of the naive hope and promise of first love.