I drink my share of Diet Coke and also augment with coffee. Yet whenever I travel, especially to a part of the world where soda and coffee are hard to get, I just do without with no real side effects. Maybe 1 day of dragginess, but not the severe headaches that some people get when they try to (or are forced to) go cold turkey. When I travel I drink water (and, uhhh, wine) and come home fully detoxed from caffeine.

Yet when I get back into my environment of huge drinks for a dollar and free refills, I always start using again. It's definitely a mental habit for me...tough to break.