The next time you buy a large popcorn at the movies, consider saving the tub. After you wipe it clean, the neighborhood kids can use it as a fort. Here's another tip: When enjoying a muffin at your favorite coffee shop, be sure to lift with your legs, not your back. From family restaurants to theaters to the frozen food aisle, portion sizes are expanding at an alarming rate. Not coincidentally, so is the typical American waistline. For all of the current talk about fats and carbohydrates, portion sizes may be the real cause of the obesity epidemic. How much do you know about healthy portions in a super-sized world? Take this short quiz to find out.