As I am having to adapt to a household of one, I'm finding it quite hard to break previous habits and buy food in smaller quantities. I used to have a huge kitchen, with a huge fridge and chest freezer so I could buy in bulk and store it before it went off. I very rarely threw food out, helped by having a husband that had hollow legs so we never had left overs.
Now I have a smaller place and have nowhere to store multibuy items. Even standard packs of food are too big for me. I bought some pesto and it did me nearly every meal for a week. I can see the temptation to put a bit more pesto in each meal so that you use it up quicker and if you took that approach to everything then the pounds would soon pile on.