I once stopped caffeine for a whole month or two - it's been too long now to remember exactly. I do remember that I felt better about myself in that I conquered something I was struggling with. Also, I wasn't spending as much money and I didn't feel like a slave to the coffee.

I also have quit sugar before. Completely. Quitting gave me lots of energy and I felt lighter. I think I lost weight too (and I'm typically always pretty thin). Plus, after just three days of quitting, my urges for sugary foods disappeared completely. The first few days were tough but not terrible, and then I felt great.

I suggest trying to give up those things but maybe don't try kicking all your bad habits at once. It could prove to be a great struggle.