I tend to take a lot of little nibbles throughout the day. To make sure that I account for those snacks I premeasure a portion of each go-to snack food. Now I can track exactly how much I have eaten. I can count the full portion on one day or break it up over the 3-4 days it takes me to eat it.
I was amazed at how much dry cereal, granola, and mixed nuts I was actually consuming. If the portion is 1 cup and you finish that cup in 3 days, count 1/3 serving each day.