Hmmm... luckily I didn't have the smoking thing to get past, but I also LOVE a glass (or 7) of wine, as well as harboring a small addiction to caffeine, so the alcohol and the caffeine were the hardest for me.
The other thing you could try (I'm doing it now as a way of easing myself out of the Master Cleanse) is Oxy Cleanse (or really any type of 'soft' magnesium based bowel cleanse). Some people say that they're a waste of time, and that the concept of built up waste in your colon is BS, but they work for me, and that's really my prime concern, so there you go! I use: http://www.earthsbounty.com/oxy_cleanse.htm
- here are a couple of reviews: http://dualcleanseaction.org/oxy-cleanse-review.
Probably to get the full benefit of a cleanse you'd want to cut back on the alcohol and smoking, but in my view something has to be better than nothing!