I tried eliminating caffeine and was NOT happy. Headaches, plus I was depriving myself of something I really enjoy (Diet Coke) that isn't the worst thing I could do. So, after the third or fourth day, I went back to Diet Coke and now that I am at the end of the first week of Phase 1, I've lost 10 lbs, so I haven't seen the negative effects. (I've read a couple of things stating that while caffeine can influence insulin production and your metabolism, the results are negligable at most.)
Splenda and Equal have 0 calories, I believe, so I think you are okay with them in iced tea (I did find decaf iced tea to be a help).
I got rid of ALL sugar and white flour and rice, etc, as well as all forms of alcohol. I feel a few Diet Cokes a day isn't going to kill me, and will go a long way towards keeping me sane. It may not be optimal, but I really don't think it is going to completely derail you, either--maybe just try to balance the consumption by keeping up with your water drinking, as well. (IE, don't let the coffee or diet soda or whatever become a replacement for the water.)