Memory
The title of this poem is Spanish for memory or recollection. The poem is exactly that: a recollection of a great moment in time in the past. The theme of memory is cemented through the repetition of the same two opening lines in each stanza. This device is used to emphasize just how satisfying the actions of the past are in the present-day when the speaker recalls them. The insistence upon being both merry and tired essentially translates into the latter-day vernacular of "a good kind of tired." With the passage of time, the speaker probably has forgotten just how worn out they really were and is remembering as a mingling of merriment which left them exhausted.
Simple Pleasures
The events that are being recalled at some unknown point in the future are not exceptional. They are, in fact, exceptionally mundane. It would likely be referred to as a "cheap date" because it involves inexpensive public transportation, free entertainment offered by nature, and nothing but fruit to eat. The narrative is a portrait of two people having a memorable time together simply as a result of being together. What they actually do is of no real significance. Until the very end, in fact, they seem to act as though they oblivious to the rest of the world.
A Rejection of Consumer Capitalism
Millay was a famously liberal-minded writer. Throughout, the poem presents two people who reject the fundamentals of consumer capitalism. The couple's insistence upon simple pleasures is not portrayed as the result of necessity, but choice. They actively seek to avoid needlessly consumption of entertainment demanding an admission price. By the end of their day, in fact, they have enough money left over to buy a newspaper they have no intention of reading simply for the sake of financially assisting an old woman. They then give her the fruit they bought but haven't eaten and top things off by giving her all the money they have except for the cost of a subway home. It is not just a rejection of consumer capitalism, but an endorsement of socialist economic ideology.
