I used to rarely drink soda (only when I went out), but now that they give it to me at the office, it's a bit tougher to avoid.

What I've found helps me avoid the temptation is really good green tea -- I keep a tin of it on my desk at all times. It's ultra-natural, both in how it feels/tastes and in reality; it's got a bit of caffeine, but nothing that'll end in a crash; and it tastes good whether it's hot or cold!