Dave Bonta's "Student days" looks back on a time of being short of money but rich in reading. The first line sets this up with a twist on the saying "the world is my oyster": here, books are the oysters, the thing the speaker feasts on and finds treasure in. Since money is tight, books seem to stand in for the wider world of pleasure and opportunity.
The speaker says he was "content" to stay indoors all day in a gown, which suggests a cozy, absorbed life of reading, perhaps a bit shabby and unconcerned with appearances. The last image changes the feel. Going out "with my legs / into the cold" leaves the legs oddly bare and exposed, as if the gown is all he has and the body is simply pushed out into winter. The tone is affectionate and gently humorous. The speaker seems to remember the discomfort fondly, as a fair price for a mind well fed.