What poetic devices can you find in here?

Laura is mistaken. Alliteration is the repetition of consonant sounds at the beginnings of words. The words "giant," "garden," and "gnome" all start with the same letter, but they start with three different sounds -- a soft "g" or "j" sound, a hard "g" sound, and an "n" sound. (But there is alliteration in the phrase "done for the day," which repeats the "d" sound.)