Never eat from a can, box, or bag as several clinical studies have shown that people will eat more food IF more food is provided or when no ‘serving’ is predetermined. This is one reason why people sometimes consume an entire bag of chips, a full container of ice cream, or a whole pizza in one sitting (mindless eating is another common reason). Yet, even people with great willpower will often eat 10% or 20% more food when eating from a bag or box without realizing it.
The simple solution is to decide how much food you plan to eat at that meal before you start eating, serve it to yourself on a plate or in a bowl, and then only eat that amount. Of course, when eating leafy green veggies or other raw produce, that serving can be enormous as those foods are very low calorie. Nevertheless, it is a good habit to always eat your meals from a plate or bowl.