The problem with restaurant lunches is that they are so BIG! And I feel compelled to eat it all. It's my mother; she did this to me. "You have to clean your plate or you're not a good boy." I never understood how my cleaning my plate would help starving children in Africa. I guess I'm supposed to be eating for them or something. It doesn't matter; it's the way I am.
When I was in Russia a couple of years ago for the Moscow Knife Show, I ate at several what would be described as cafeteria-style restaurants. Everything is weighed and sold to you by the gram. Softdrink glasses have a line etched on them and the clerk carefully fills the glass exactly to that line and not a drop extra. Why? Because you are actually paying for the food, that's why. In America, the food is a minor component of the cost of a restaurant meal; what you're really paying for is labor. But, many people still judge the merit of a restaurant by the portion size, "Oh, you get your money's worth that that place." So, the restaurants pile on the food because, compared to the labor, the food doesn't cost them very much.
In America, if you go for fast-food, they throw the cup at you and tell you to go and fill it yourself. Why? Because if you put your head under that machine and pushed the lever in and just let the Pepsi flow into your mouth and drank it as it came down, you would die of water poisoning before you'd consume enough Pepsi to cost them as much as the labor to fill one or two cups costs. They are dollars ahead to give you free refills -- all you can drink -- if only you'll do the labor of filling the cup yourself.
And so say, "Yes, I would like fries with that," and enough fries arrive to feed a small third-world nation for a week. And I feel obligated to eat them all.
As a result, I make my own lunch whenever I can.