Saw a guy today at the GC load his bag with 2 dozen balls. (New Tour response)
I asked him why so many? He replied that if he hits one cart path, tree branch, root, or hard packed area, that he plays a new ball, then just bags up the "used ones" and gives them to the high school team.
I'm sure we all have had a ball hit something playing a round, but 90% of the time there's no damage to the ball, and still very playable.
So how many balls do you pack for a round?
I have 12 usually. 6 for the round, and 2 sleeves incase a friend needs a new ball.
I carry 2 of them in my pocket though.