Remember kids adults dangerously close to popping out unwanted kids, Don’t talk to the police
This.
Don't be friendly. You didn't just come from a friend's house. Because for all you know, the cops may have been staking out his house, and if there's actually any illegal activity going on there, you just implicated yourself as being a part of it or at the very least a customer, whether or not you were actually there to engage in illegal activity or actually just visiting a friend.
Whatever that smell is, you don't smell anything. I don't care if it's a funky air freshener or you're carrying a truckload of weed. You didn't smell anything and you've never so much as smoked a joint in your life. Saying "The last time I smoked was......." is admittance that you use controlled substances and in some cases could give the cop reason to believe that you're still under the influence.
No, you don't know exactly how fast you were going because you're paying attention to the road, not the speedometer. You were just going with the flow of traffic.
I don't care if you were supposed to be there half an hour ago. You're not late for anything. Asking the cop to hurry or whatever because you're late is just going to get him to intentionally take longer either just to make your life miserable or in hopes that you'll become frustrated and start saying things you wouldn't normally say so he can get more info out of you.
And I fucking hate Hate HATE the "ask if you're being detained. Ask if you're free to go" advice. All this does is antagonize the cop. All it does is make them believe that you're nervous about something, and they're going to want to know why. And if you start off the conversation being adversarial like that, the cop is much more likely to try to make your life as miserable as possible. Watch an episode of COPS. When most people try this line of defense, they often do so in the most unnatural way possible, acting as if they're still in the process of memorizing a script. It just gives off the impression that you have something to hide. The only time you should ask "am I free to go" is after the cop already gave you your documents back and you're just clarifying whether or not he's done yet. The only time you should say things like this are when they are a direct response to a cop's question or actions where that kind of response would be appropriate. But randomly blurting out "Am I free to go? Am I being detained? I do not consent to this!" or other lines at random just pisses the cop off and gives them the idea that you've got something to hide. So what do you say instead of that? FUCKING NOTHING.
If it's truly just a routine traffic stop, give them the documents, say nothing, take the citation or whatever, and be on your way. Take the rest of it up with the judge. The only time you should be saying anything at all, is if it's absolutely necessary and if it looks like it's going to go beyond just a routine stop.
I've seen too many people either try to be overly friendly, believing that if they're forthcoming the cop will work with them, or just argumentative and turning what would have been a routine citation into an arrest because they either admitted to actual crimes they committed in the process or got a little too argumentative with the cop and ending up in cuffs and facing an obstruction charge.