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).