Sugar cereals, cookies, candy, saltines, potato chips, white bread, white rice and pastries are all simple carbohydrates. They will cause a spike in your insulin levels which will and does slow down your metabolism and your energy.
Throw it all out: white bread, white pasta, white rice and replace with whole grains. Choose whole wheat pastas, brown rice, and whole wheat breads.
It will make a difference in your energy level and the rate your metabolism burns.