Whole milk, drink as much of it as you can each day, it is high in protein and is a great bulking food.

I know a friend who drinks one gallon of milk per day.

Is it true that milk has growth hormones in them?

I've been drinking a whole gallon of milk a day for 6 months now, the results have been amazing. Cows are often given growth hormone, so there is probably at least a trace amount of growth hormone in milk. Probably not enough to affect a human being.

GH is not orally bioavailable anyway, so it hardly matters what they are taking.

Just eat high calorie foods. If you add 500 calories of donuts in your 3rd meal of the day (lunch) or add some milk, or some EFAs at every meal then go for it. Whatever it takes just add it up all up.