Often a group of my friends will leave a party to smoke cigars/cigarettes. I do not smoke and have no interest in picking up the habit but I would like to be included in the conversation that happens while people are smoking.
How do I politely, yet firmly say that I will not be partaking while still being able to be in the same area where I will be offered cigars/cigarettes?
When someone heads out to smoke, they often announce it or extend a general invitation:
Time for a smoke. You coming?
You are not restricted to "yes" and "no" when you reply to one of these. Try:
I don't want a smoke, but I'll come with you.
While you are out there, it is natural that if someone sees you are not smoking, they assume you have run out, and offer you one. Just say "no thanks" when they do. The offer is intended to be polite, not to change your behaviour. Even if they know you don't smoke, they may feel compelled to offer rather than consume in front of you, and you don't need to make any kind of big deal out of declining.
There's no need to be "firm" or to make sure all participants know in advance you will not be partaking. You may meet someone who comes from a culture that offers multiple times even when you say no. If this happens, or for any reason you're not feeling comfortable with a simple "no thanks", try:
Honestly, I'm just here for the company.
Smile (genuinely) when you say it. Nobody can be offended by that.
I don't see any evidence for peer pressure in your question.
I for one do not smoke, but I hangout with friends when they do. I'm usually there for the fun conversations, and they don't have to offer me a smoke, because they know me well, and that's how friends are.
If you're in a new circle of friends, though, they might offer you a smoke as a friendly, polite gesture, and in such cases, you can politely decline the offer: "thanks, but I don't do this", and resume the fun conversation.
If it's a case where you're sort of pressured into smoking (or doing something you don't want to) then that's a real problem, and beyond the scope of this discussion.
I can only speak from what I have seen socially, which is that most of the time an offer for a cigarette or beer is merely that, an offer. I do not think that most people want you to say yes, but they do not want to appear inhospitable. If it doesn't bother you to be around people while smoking & you would like to go outdoors with them, then I do not see anything that should be an obstruction. I am constantly offered things I do not want when in social gatherings & a "no thank you" has always worked fine. I do not drink when out & sometimes get a little bit of teasing, but I always just reply that they will thank me when I am driving their drunk behind home later.
Often time any pressure we feel socially is internal, even when it feels external. Someone can try to even go so far as to talk you into something, but if you put no weight on their impression of you, then you will often feel absolutely nothing no matter what they say, other than perhaps irritated that they do not drop it. You are more likely in that case to think that person nags you, versus that you are being pressured. If however, you value that person's feelings about you, you can feel pressure where none exists, simply by your desire to get some sense of approval or inclusion. It is best them to assume that you are included even if you do not partake in every part of that socializing practice if you are not being told there is something you must do in order to be included.
A bunch of people I worked with used to go to happy hour after work all the time & I didn't want to. They didn't realize I don't drink & interpreted my not attending as being anti social. I quickly realized I can go & have a soda & they were just as happy with that as if I had drinks with them. I had no idea I appeared stand offish to them. Likewise, people offering you a smoke, likely have no clue it feels like pressure. I didn't even feel pressure to go. I had nothing against going, but I didn't see the point. Once I realized they were seeing it as me not liking them, I modified & it was fine. I still didn't go all the time, but went often enough that it made my work relationships more amicable.
There is no need to state anything unless someone asks if you want a smoke (no thanks, I'm good), or why you are out there if you don't smoke . In that situation a joke like I needed some fresh air works. You can also use a different item to deflect a bit, like taking a drink/soda/beer with you in your hands. No one really cares enough that you are going with them while they smoke.
Or find friends that don't have filthy habits.
