do something for luck
1. With the belief or expectation that one's actions will bring good fortune. A: "Because our team won today, we all have to wear the same clothes to next week's game for luck!" B: "Don't you think you're being a little superstitious?"
2. For no apparent reason. Well, little brother, there's your 12 birthday punches—oh, and one more for luck! I was so exhausted after running all those laps that I nearly collapsed when the coach said "and one for luck!"
See also: luck
do something for ˈluck
1 do something because you believe it will bring you good luck, or because this is a traditional belief: Take something blue. It’s for luck.
2 do something for no particular reason: I hit him once more for luck.