I found somewhere what was called "Scam IFS". The recipe:
Breakfast, lunch and dinner - all 3 options at lowest quality, but set at highest possible charge (50, 70 and 90$)
Snacks - all 6 options, highest quality, 0$
Everything from next page checked and 0$
That somehow gets you 3 stars and 410$ profit per passenger
You can get a somewhat profitable (and more realistic) IFS by giving them a couple meal options and charge 4-5 dollars more than its cost, a couple of few snacks, free newspapers, and charge for souvenirs and entertainment packs (again 5-6 dollars more than their cost).
I also have a question... in an old airline that I bankrupted mainly from this, I opened a hub and I wasn't getting any connecting passengers. What's going on? Was it that I had a 100% loadfactor anyway and it wouldn't change?