Not a cop but a former good friend of mine is a police officer in Los Angeles. At the time, he was working a type of gang-unit in a particularly bad part of the city. He told me a story of a time he was doing what I think he called 'information checks' in which they walked patrol of the neighborhoods of their beats, just having conversation (if they could) with people they'd happen upon. This isn't exactly a 'stop and frisk' but was kind of like it. It was usually people they knew of and/or were asking questions about other people in the neighborhood.

In this instance, I think there was a guy wearing a backpack who reeked of marijuana and so they stopped him to ask him about it and wound up looking through his backpack. My friend dealt in homicides and crack arrests mostly so he wasn't going to stress this guy too much about the weed. If he only found a little bit, he was going to let the guy go and maybe even let him keep the weed. Except the guy is acting excessively nervous. My friend kept telling him to relax and that it was only weed and so it's not that big a deal. My friend found a can of coca cola in the backpack and said something to the effect of "here man, have some of your soda and calm down" and he realized it was one of those fake coke cans, and it was full of ecstasy pills. I don't recall the amount but it was something like 50 - 100.

My friend said if the guy had just been chill, he might not even have looked so closely into the content of the backpack- he just wanted to make sure he didn't have a ton of weed that he might be selling. Turns out, the guy was selling ecstasy and went to jail for a long time.