I weigh EVERYTHING I eat, whether it be a couple slices of tomato, or a teaspoon of low-fat soy milk. A calorie is a calorie is a calorie. I don't use guess work because more often than not, where it comes to guessing the weight/size of our food, we are generally way off base, and not in our favour :-( All these little things add up, and can make a difference between losing and gaining!
As far as the foods are concerned, below is a link that you may find helpful if it isn't in the SP Data Base. Just enter the food in the search bars at the top of the page. nutritiondata.self.com/