I know I am a jackass for saying this, but the best thing that a policeman can do is leave people alone.
If you're not breaking the law, you expect to be left alone. That moment of uncertainty when a policeman stops you or approaches you is stressful enough. There are times when you don't want to inadvertently scare people by introducing authority figures into their daily routine.
Really, free stuff is just not worth the aggravation. Leaving people alone is a priceless practice in modern American society.