The first thought that came to my mind after I picked up on the punch line at the end of the poem was that all of the things listed as being candidates for "the best thing in the world" are said by the poet to be "out of this world" not only because they are wonderful and greatly desired, but also because they are impossible. However, this thought disturbs my optimistic tendencies. So, my new interpretation is that, although the listed wonders are "out of this world" in that they may not currently exist in our lives, they are the attainable goals of the optimistic and romantic.