Giving in to those temptations: cigarettes, eating another slice of pizza, etc. won't help you feel less stressed or frustrated. I think it's great to let your feelings out--don't bottle them up--and then do something that will help you de-stress. A walk, a bath, some soothing music, something you enjoy...
Finding ways to relax will help will help you reach your goals without doing something that will make you feel regret or more frustration for giving in to the temptation.
I quit smoking over 5 years ago and the desire will come back but giving in to it doesn't help me feel better. Stress eating doesn't release stress, it causes more of it.
Hope you feel better!