"a silver tag with the legend: Drink me, while the cover of the silver dish was engraved with the exhortation: Eat me"


This is a clear reference from 'Alice's Adventures in Wonderland' by Lewis Carroll, which is a tale firmly in the public consciousness, perhaps as much so as the traditional folk stories Carter explores.  When Alice follows the white rabbit down the burrow, she finds herself in a hall, surrounded by a number of locked doors.  She finds a key which fits one of them, but the door is too small for her to fit through.  She then notices a bottle labelled 'Drink Me', which makes her shrink so small she cannot hold the key.  A cake labelled 'Eat Me' then causes her to grow so large that she hits her head on the ceiling.