A wedding favour is a small gift given by the a married couple to guests, as a mommemto of the day, at their wedding reception (or at the ceremony itself).
The tradition is an old one (some say dating back to the Romans) common among European aristocrats - particularly Italians where the wedding favour was known as a bonbonniere. A bonbonniere is a trinket box filled with delicate sweets or sugar cubes. The box itself was decorated with precious stones and crystal. Read the full weddings favours article