Cheat extra calories into your meals. Anything with an oil as its base, dressings, Ranch especially, Mayo, aioli. A 1/2 cup is over 500 calories. Heavy cream and butter in everything. Making a spaghetti sauce? Add heavy cream and make it a blush sauce. Mac and cheese? Full stick of butter, make a roux and add heavy cream to the mix. Dont sleep on Ketchup and BBQ Sauce as a condiment either, both have sugar or corn syrup as the base.
Beverages. Do not drink anything that doesn't have calories. Milk is a gainers best friend as it hydrates you as opposed to soda with caffeine. Sweet tea and full sugar koolaid is good too.
The other big key is eating when you arent hungry. Driving in a car, snack. Sitting watching tv, snack. Doing chores, have a snack with you. Most supersized people eat huge meals, but they also snack constantly throughout the day. They say they don't eat alot, but if they eat once an hour the entire time they are awake, they have eaten 16 times.