Everything is ok in moderation, but a coke a day isn't moderation. I don't drink coffee and rarely drink coke, and that would be sometimes from a fountain when I eat out. The thing here is to remember if you stress so much over what your drinking (or even eating for that matter) you will certainly have some stress related health issues. Relax, eat and drink what you want, but only in moderation. Diet's DO NOT work, and if you go on any type of diet and lose weight, you will most certainly gain it back, plus more. Just eat more fresh veggies and fruits daily and try to stay away from fried foods, sugars and startches....or at least cut way back.
Excercise is extremely important. Make sure you break a sweat once a day or swim a few laps each day. Wish I had a pool, but I do get on the tread mill and on my bike.