We homeschool... so we have lunch at home almost every day. We go out to lunch once every 2 weeks, and picnic at the park in good weather. I love to cook, but get seriously tired of it (hmmm does that make sense?), so I do "easy button" as much as possible.
I'm a big fan of dinner leftovers for lunch the next day (works killer for preschool, as well, because you know they'll eat it). We also freeze soup portions whenever I make a big soup... so right now we have 6 or 7 kinds of soup in the freezer. Soup and sandwiches are a very common lunch for us. As is "brunch for lunch". We also have a panini press I couldn't live without... we do baguette grilled cheese all the time (it's super easy to grown-up-ify with that one, he can have mozzarella every day if he really wants, but I can throw in some blue cheese and pear, or cillantro/ jalepenos/ ham, or arugula roast beef, or tomato/basil/mozzarella, or or or). We also do a lot of asian bento. Whatever it is though, lunch has to be E.A.S.Y. Hence why lunch usually springs from altered leftovers or the freezer.