You either cook everything yourself and weigh every ingredient. Or you buy totally packaged meals (Lite 'n Easy, etc), or you buy fast food (And even then, the calorie counts in fast food are... inaccurate at best).
If I go to the corner shop and get a sandwich I have no idea what's in it and there is no accurate way to estimate.
While it's good to be aware just how energy dense foods are (like muffins... aka breakfast cakes) there is no method that I'd consider both achievable for the average person to consistently do AND accurate enough to be considered 'counting' as opposed to washy estimates.