i need to eat more calories than i burn.
Both protein and carbohydrates have 4 kcal/gm.
Fat has 9 kcal/gm.
Fatty foods are the densest source of calories.
If you want to stick with healthy fats than there is avocado, olive oil and nuts.
Of course most people have the opposite problem; eating too many more calories than they burn.
When I was a competitive bicycle racer in my mid 20's I found I couldn't consume enough calories to maintain my weight when I ate low-fat.
I haven't had that problem since though.
Carbs are really good for that, pastas, bread, etc. You dont want to eat junk food because its counterproductive and unhealthy calories, stick with carbs, proteins, fruits with natural sugars, nuts, peanut butter, etc.
Cheesecake!! That's what I'd eat if I needed more calories....that and icecream ....milkshakes....Oooo, the list goes on and on :)