Milk isn't good for you anyway, so that's no loss, and it doesn't really add weight all that much unless you eat a ton of it. But here's the thing -- unless you have a physiological condition that prevents you from absorbing the food you eat, and that is a condition that exists, eating more of anything will help you gain weight. The more food you eat that metabolizes quickly into sugar or contains high fat will likely help you to gain weight. That isn't a healthy way to eat, but if all you want is to gain weight and your body can process what you eat, just eat more than what you're eating now. But know that gaining (or losing) weight fast isn't healthy and might not last. Also, the weight you gain will be fat unless you go on a program of resistance training. But if you just want to gain weight fast and don't care about your health, eat a ton of fattening food.