The poem is a single sentence broken into tiny lines, and it reads almost like a riddle about what makes a person happy. The speaker lists things we usually chase: to play, to gain, to own. Then comes a twist. "No money exceeding" suggests that having no more than a little, or perhaps no money at all beyond what's needed, is enough. The result is that the speaker is "merry" and sings.
The title, "Plenty of Nothing," plays with the idea that having almost nothing can feel like abundance. The speaker seems content, even cheerful, and not at all bitter about being without wealth. The short lines make the poem feel light, like quick steps or the notes of a little tune, so the mood is playful and carefree. You can also read the words in a looser way, since the lines don't spell out every connection. That gives the poem a gentle puzzle quality, but the feeling at the end is clear: the speaker sings, and the singing is the point.