I have smoked but never got into the habit because I hate the craving. As soon as I'd start craving a smoke, the sense of loss of control would turn me off and I'd stay off for months. About the only time I smoke now is if I'm with a bunch of people who are smoking and getting cancer anyway, might as well enjoy it. However, that is becoming rarer and rarer as fewer and fewer of my friends smoke.
Weed, never been interested, had it a bunch of times, it's never done anything to me at all. I only smoke it to shut up other people who won't accept that I don't get a buzz off it. Very rare.
Alcohol - sure why not? If I have some I'll usually have a few drinks a week, it's actually proven to be a health benefit in moderation.