Alliteration is the term given to repeated consonant sounds at the beginning of words that are close together. This is a key technique that is used by many poets to create word music and also make the phrases stand out. Consider the use of alliteration in many headlines in newspapers. Alliteration gives those words a greater impact.
Considering the poem, you can see that there are many examples of alliteration, including "Lurk late," "Strike straight," "Sing sin," and "Jazz June." All of these, combined with the short, sharp, snappy lines, give this poem a real slick feel and help us to imagine the "coolness" of the speakers, before, of course, the devastating ending really communicates their end by following such a lifestyle. Thus the use of alliteration in this poem creates music, giving the message and the theme much more emphasis as we read and hear the poem.
As the repetition of an initial consonant sound, alliteration catches the ear and speeds the movement of the line of poetry in which it is contained. In Gwendolyn Brooks's short poem, "The Pool Players/Seven at the Golden Shovel," referred to as "We Real Cool," alliteration also enhances the musical quality of the verse throughout every line but the last, endowing this literary device with the tonal properties of jazz.
Jazz is a musical art form that challenges traditional music through its licks, sounding like skipped heart beats, as in "lurk late," "thin gin", and its inventive improvisation, as in "Strike straight," "Sing sin." This tonal property often breaks the regularity of rhythm earlier established in the poem. Alliteration's musicality gives a certain rhythm to the poem along with a feeling of doubt, which is followed by the abrupt ending line that breaks the speed built by alliteration and breaks the musicality, as well as breaking the shockingly "cool" tone with "We die soon."