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.