I've nearly always prepared my own lunch under the belief that I can then both control what goes in it and how much I want to spend.  Suffice to say most days this consists of a sandwich and there is a daily unsaid ritual of comparing your own lunch with that of your colleagues around you.  Little did I know that famous economist Daniel Kahneman has put some thought into so called Sandwich Envy:

When you make your own sandwich, you anticipate its taste as you’re working on it. And when you think of a particular food for a while, you become less hungry for it later. Researchers at Carnegie Mellon University, for example, found that imagining eating M&Ms makes you eat fewer of them. It’s a kind of specific satiation, just as most people find room for dessert when they couldn’t have another bite of their steak. The sandwich that another person prepares is not “preconsumed” in the same way.

So because I make my own sandwich, and have therefore thought about eating it whilst preparing it, I confine myself to lower levels of enjoyment of said sandwich when it comes to eating it.