WordNet records no synonym and no antonym for lucky dip. It is the only member of each of its synsets, which is common for technical, taxonomic and single-sense vocabulary — there is no other English word that means the same thing. The broader and narrower terms below are the useful relations in that case.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
a game in which prizes (e.g., candies or coins) are concealed in a container and for a small sum a player can draw one out at random
a selection or decision purely at random
“their system of hiring people seemed to be a sort of lucky dip”
Synonyms, antonyms and the broader and narrower relations for lucky dip come from Princeton University’s WordNet. Full sources and licences.