All great options, I've heard Prime is the best supplement for increasing appetite, not speaking from experience though...
So great advice in here. Some other options would be trail mix (1cup = 640cal), adding a glass of whole milk to each meal (1cup = 160cal), making gainer (or purchasing them), peanut butter (2tbsp = 190cal)
GL man, try increasing your calories though.. I've found it difficult consuming my caloric needs (currently eating 5,300cal/day) initially, but after 3-7 days I find it MUCH easier to consume, and also VERY hungry if I don't.
Timing is very important too (not because you'll go "catabolic" or w/e), but if you're consuming a lot of cals (or a lot to you for that matter), spacing your meals out @ the right times, will make them much easier to consume. If you eat 1000cal every three hours, you'll easily be able to have down 4000cal in 12hrs (or whatever calorie/time interval you wish; 500cal every 1.5h = 4000 in 12h, 800cal every 2hr = 4000cal in 10h, etc)