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. Used to describe something done for no apparent reason. Similar to the phrase "just because." 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.