"don't worry about my lunches out, I usually go to the supermarket and just buy a salad"Um, about that salad....
You see a newspaper in England decided to put some of those supermarket salads to the test. They bought a bunch and had them sent to nutritional labs for analysis.
The results (click the photo up top to see them enlarged)?
More calories and more sodium than Big Macs with comparable amounts of saturated fat (though greater amounts of healthy unsaturated fats).
As always, calories and nutrition are not intuitive. The only way to truly know what you're having is to make it yourself.