I am bit puzzled. Why do you need more calories? You can eat lot more vegetables and fruits to get calories.
Most importantly you should think micronutrients and eat as much as you want to. The three macronutrients are fats, carbohydrates, and proteins. Each of these nutrients provides calories and helps you carry out essential functions like walking, thinking, converting food into energy, growing, and repairing yourself.
Fat is the most calorie dense nutrient, providing 9 calories per gram. Carbohydrates and protein both provide 4 calories per gram.
Micronutrients are also essential to your body, Micronutrients are usually called vitamins and minerals. There are 28 essential micronutrients your body needs to survive. If your diet does not supply enough of the critical micronutrients, your body will use up any storage supplies of the vitamin or mineral (which can cause bone loss and muscle wasting). You can experience vitamin deficiency diseases.
Nuts are some of the most calorie dense foods and with good fats that will help repair your body. Avocados and mushrooms are also high calorie foods.
I always say what does an elephant eat? What does a horse eat? We can get energy from vegetables and fruits and don’t have to worry about what will happen if we don’t eat meat.