The correct option is A packet
'Plague' refers to an infectious disease that is fatal, it does not relate to candies, hence B is incorrect.
'Wisp' refers to a thin strand or a bunch of something, examples: wisps of hair fell down, a wisp of thick smoke came out of the chimney. It does not refer to mints (which are sweets) hence C is incorrect.
'Prattle' expresses an action of talking (in a quick, foolish way), it has no relation to mints, which are a food item. Hence D is also incorrect.
'Packet' refers to a paper or cardboard container that is usually used to carry something, like food or other goods. When used here, it refers to a carton filled with mints (packet of pints). Hence this is the most suitable option and A is correct.