If I drink 1 cup of milk each day..,,?!

You dont get much calories from milk evenm the full fat stuff, Yes id try carbs like pasta, potatoes, some meats, bread rice etc. Good for keeping off the junk food thats gonna help your general well being.

If all you are eating/drinking over and above your normal daily food consumption is one glass of whole milk, you are only adding about 150 calories a day to your caloric total. It takes 3,500 unburned calories to put on a pound of fat, so it would take almost 24 glasses of milk (8 ounces each) or more than 3 weeks to add one pound of fat. If you want to add lean body mass then that is a totally different issue, requiring regular exercise and higher levels of protein in your diet.

It doesn't matter what you eat, its the total calories over and above what your body burns each day that will determine wether you gain, loos or stay the same. So one donut may be 300 calories, and two glasses of milk will also be 300 calories, Of course you are way better off to drink the milk, as at least it has calcium and has vitamins like vitamin D, whereas a donut is about the worst thing I can imagine eating (deep fried refined wheat flour coated in refined sugar).

Try eating more healthy fats to add calories, as fat has 9 calories per gram, and protein and carbohydrates (starches and sugars) have only 4 calories per gram. Things like avacados, nuts,
seeds, olives and fatty fish like salmon are great choices and are exceptionally healthy foods.
Of course, avoid satured fats and trans fats to keep your diet healthy.

3 cups of milk a day, actually, for strong bones. Eat lots of vegetables and fruits, and whole grains as they have more calories and are more nutritious! Put butter on your bread, use olive oils and healthy fats, make sure you have 6-11 servings of grains a day, protein like chicken, pork, fish, steak, peanut butter, etc... You can have some junk food once a day or twice, just not a TON.

Exercise, too. Just make sure you eat when you are hungry. But not to point you are stuffed.

Eat pasta, breads and carbs.... and alot of them. Eat them before bed so you don't burn them off.

Eat more whole grains