Interesting intellectual puzzle. I've never smoked, so I'm going on observation, but if it ever came up in a game I'd probably accept the following handwave:
One move action to retrieve the pack and extract a single cigarette.
One move action to re-stow the pack and place the cigarette in the mouth.
One move action to retrieve the matches or lighter and prepare to create flame.
One standard action (draws AoO) to create flame and properly light the cigarette.
One move action to re-stow the matches or lighter.
Though it hasn't been mentioned, I'd probably insert another standard action (draws AoO) for cutting a cigar and two move actions to retrieve and re-stow the cutter.
In the event that keeping track of how much time it takes becomes important, I think losing two and a half rounds to light a cigarette (four for a cigar) sounds about right. It seems to me that it'd take noticeably longer than drinking a potion because all you have to do with a potion is get it out, open it, chug it, and drop the bottle. Of course if the player raises a hullaballoo ("but just look at all the different things I have to do!") I could be persuaded to make it cost twice as long instead.
If there's some reason the character needs to do it more quickly, I might call for a moderate DEX check (DC 15 or 17 or so) to do it a little quicker at the cost of attentiveness to surroundings:
One full-round action (draws AoO) to get out the pack, place the cigarette in the mouth, and re-stow the pack.
One full-round action (draws AoO) to get out the lighter or matches, light the cigarette, and re-stow the lighter or matches.