When I learned of my pregnancy, I was drinking one small pot (I have a personal four cup coffee maker) of coffee a day, maybe two and one diet cola a day. The diet soda was the only pure junk item I was still consuming on a regular basis. When I learned of my pregnancy, though, things changed. I started to mix half decaf and half regular coffee (more regular than decaf) and cut my sodas to just a few times a week. Eventually, I eliminated all soda, for the most part, from my diet. My husband wasn't happy about that only because we stocked up on caffeine free diet sodas (root beer, lemon lime, cola) and in February and March and moved several cases in August, on which I'm still working. Since soda is pure junk, I quickly decided that my baby did not need that. However, the diet Sierra Mist did help my heartburn, which was chronic my last month and a half. (Vanilla soy milk and natural diet Hansen's Ginger Ale also helped.)
Even during the first month and a half of my daughter's life, I still did half and half coffee just a few times a week. Actually, the first post-birth cup I had was two weeks and three days after she was born, as I had met with some friends at a local coffee house and treated myself to a cup of half and half. It wasn't until she was a couple of months old that I went back to a pot of regular coffee daily. In the evenings, when I want a hot drink, I make decaf, still, though a couple of times, it's been a full scoop (two tablespoons) and a about a tablespoon of decaf and about a tablespoon of regular.
For the most part, I stuck with whole, real foods during my pregnancy. There were a few times I compromised, eating stuff I wouldn't have touched otherwise, like white bread. I figured some food was better than nothing. I would then make up for it by eating some whole wheat bread later in the day.
When in doubt, ask your doctor.