In BrE, fag is a common slang word for cigarette.

In Britain the vernacular (on the street) term is fag.

So many: butt, cancer stick, gasper, rollup, smoke, cig, ....

Yahoo Answers has a brilliant "best answer" to this question that I would love to quote in full, but I would probably get into big trouble with the mods.

Don't forget about coffin nail.

I'd support @Mick and @WS2. For the many years that I smoked (in India), fag was what the 'cool' guys called it.

From what I know, very few in America would use "fag," given the homonymy with the slur.

"the only one that I found" - How did you look?

@Drew Certainly not on Yahoo Answers.

In US English, my first thought is 'cig'.

@RichardKayser I knew we could rely on you to point out the dangers of smoking tobacco, etc. Filthy habit, what?

@Silenus - When I was young "fag" was the common slang term in the US, at least in the schoolyards I frequented. I would guess that the term dropped from common use (to mean "cigarette") about 30 years ago, however, as the term took on the (derogatory) meaning of "homosexual". I've no idea why the term acquired this new meaning. (If, eg, one were writing a book set in the US in the 50s, "fag" would be the word to use.)

@JEL - Yeah, "butt", "smoke", and "cig" are probably the best one can do for US terms, unless we can get a smoking teenager in here to update us on the slang.

In the UK, "fag" is widely used.