Obviously we all know the 3 major macronutrients are proteins, fats, and carbs. All 3 macros have there place in any meal plan and none should be neglected especially when trying to gain mass. Foods to meet your protein requirements are grilled lean chichen breasts, baked fish, cans of tuna, lean ground beef or steak, eggs, whey protein powder, and dairy products such as milk and cottage cheese to name a few. So if you're finding it difficult to get enough protein in for the day these are the types of foods you need to invest in.
Carbohydrates are great for energy and help the muscles to maintain fullness, although too many carbs can cause one to gain excess weight and look soft. So dont skimp out on or be afraid of carbs. They aren't your enemy unless you allow them to be. If you're finding it difficult to get all your carbs in for the day then here's a list of the best: brown rice, russet potatoes, sweet potatoes, whole wheat bagels, wheat bread, fruits/veggies, oatmeal, grits, and various types of pasta.
Fats are also used as a reserved supply of energy for the body and help to maintain body temperature which is important. Fats also contain a high amount of calories which is great for bulking. If you have a hard time getting enough healthy fats in your diet then these food items will help tremendously: Peanut butter, avocado, raw nuts and seeds, whole eggs, dairy products such as milk and cheese, vegetable oil or olive oil, and flax seed and wheat germ to name a few. All of these are comprised of healthy fats essential for filling those macros and increasing your caloric intake to put on some mass. Water is another nutrient vital for hydration, energy, and fullness not to mention all the good it does for the organs etc, so be sure you're drinking plenty of water each day especially if you're on a vigorous training regimen.
