From Thomas Firminger Thiselton-Dyer’s indispensable volume Folk-lore in Shakespeare:
Easter. According to a popular superstition, it is considered unlucky to omit wearing new clothes on Easter Day, to which Shakespeare no doubt alludes in “Romeo and Juliet” (iii. 1), when he makes Mercutio ask Benvolio whether he did “not fall out with a tailor for wearing his new doublet before Easter.” In East Yorkshire, on Easter Eve, young folks go to the nearest market-town to buy some new article of dress or personal adornment to wear for the first time on Easter Day, as otherwise they believe that birds—notably rooks or “crakes”—will spoil their clothes. In “Poor Robin’s Almanac” we are told: “At Easter let your clothes be new, Or else be sure you will it rue.” Some think that the custom of “clacking” at Easter—which is not quite obsolete in some counties—is incidentally alluded to in “Measure for Measure” (iii. 2) by Lucio: “his use was, to put a ducat in her clack-dish.” [649] The clack or clap dish was a wooden dish with a movable cover, formerly carried by beggars, which they clacked and clattered to show that it was empty. In this they received the alms. Lepers and other paupers deemed infectious originally used it, that the sound might give warning not to approach too near, and alms be given without touching the person. A popular name for Easter Monday was Black Monday, so called, says Stow, because “in the 34th of Edward III. (1360), the 14th of April, and the morrow after Easter Day, King Edward, with his host, lay before the city of Paris; which day was full dark of mist and hail, and so bitter cold, that many men died on their horses’ backs with the cold. Wherefore unto this day it hath been call’d the Blacke Monday.” Thus, in the “Merchant of Venice” (ii. 5), Launcelot says, “it was not for nothing that my nose fell a-bleeding on Black Monday last at six o’clock i’ the morning.”