A key word in that bookshelf thing was "essential" I think -- sort of like "the essential Shakespeare" including the most famous monologues and Sonnet #28.
This is an "abridged encyclopedia" approach, or rather, enforces the encyclopedic approach, rather than an inclusive "all the words" dictionary-type approach.
That it, it is a sort of greatest hits question, or an essences question.
to be or not to be; that with which to be your poetry, your poetry can't be without
so the educational poetry, the poetry you had starting out, would not be a very wrong answer
or, cheat and say every Louis Underwood anthology, every Norton anthology, etc.... (like my Poulin anthology love poems)
I couldn't have written the poems in DaDaDa without the women writers of the 13th century, the Norton Anthology, the Greek Anthology, a Palm Pilot, MS PowerPoint, some Boolean algebra. I couldn't have written the poems in Locket without the modernist poets and the New York School poets.