High-calorie & High-fat foods that are NOT dairy or sugary!?

Hi!

I suffer from IBS as well as a general difficulty in gaining weight... not sure if it's related to the IBS or not. Anyway, if I don't consume around 2000 calories a day, I lose weight - and I'm painfully thin. Problem is, I feel (and look) terrible when I eat a lot of sugary foods and dairy products... as yummy as they are (which is unfortunate because they pack a lot of easy calories).

I need a list of foods that are HIGH in calories and fat (not just protein) but that aren't dairy or full of sugar. I'd rather not eat a ton of empty carbs, either.

I just don't have the time or energy in a day to be constantly eating - but each meal needs at least 500-800 calories a day (and that's a ton of food when you're avoiding sugar-rich snacks), plus snacks in between. How can I possibly do this?? I can't eat 3,000 avocados a day! Or a pint of peanut butter between meals!

Any help would be greatly appreciated! Thanks!