The key to eating whatever you like, without gaining weight? Exercise and portion control. What you've eyeballed as the recommended 2/3 cup serving of cereal might be closer to 1 ½ cups, and, therefore, more than twice the calories. Instead of hauling out your measuring cups every time you want a snack, just use Measure Up Portion Control Bowls ($24 for set of 2). They've got measurements handily marked on the inside of the bowl, so all you have to do is pour and munch.