^Not everyone who smokes a cig ends up a smoker, although most do. It doesn't require that much discipline to smoke without becoming addicted. I've never been a "smoker" really, and I've smoked for years. Still, I smoke one cigarette or pipe bowl a day and that's my only tobacco intake. I'm not addicted, I just love tobacco. But yeah, it only requires a little will power. Cutting out caffeine alcohol or weed would be much harder for me than cutting out tobacco.
That being so, pipe tobacco>>>>>>cigarettes. Try some high quality pipe tobacco while tripping or sober, stuff's delicious and gets you a great buzz and is much better than smoking cigarettes in every way.
Weed is good for nausea but I only like to get a little stoned during trips. I'm a daily smoker and I smoke a little bit less on days when I trip. Of course, once I come down I smoke a lot more.
Another thing good for nausea, if you can find them, are ginger candies. Lots of companies make them, if you have any health food stores or asian markets I bet you can find them. Reeds makes some but my favorites are Ting Ting Jahe from Indonesia. Anyway, they taste great (if you like sweet ginger), are very chewy (which I find fun while tripping) and work great for settling the stomach. You can also boil some water, dissolve 2-4 of them in water and have a nice ginger tea.
You can also chew on a piece of fresh ginger. Or cut it into pieces and boil it in water a while, then drink the tea.
I have IBS so I have problems with nausea a lot. Weed and ginger are the only things I've found to really reliably help (other than medications, which I hate to take).