Place roast in the bottom of crock pot. If you are adding onions and/or potatoes, cut these now and place on top of the roast. Pour cream of mushroom soup over roast (and onions & potatoes). Spinkle full pkg of ranch or onion mix on top of the soup. Pour Pepsi over all ingredients. Bake in crockpot all day. If you want to start eating sooner, just cook on high. Makes 4 servings.