My sister had that surgery and she ate very, very little, and still does over a year post op, she lost 100 pounds. You pretty much have to cut out all carbs so it will literally be 2-3 bites of a protein and some green vegetables. We are talking 4-6 tablespoons of food at a sitting about 5-6 times a day if you want to keep losing weight. Since you will still be on your weight loss journey, you will not be sabotaging yourself by "cheating" most likely because it will also make you feel sick. It is not just portion sizes, it is a completely different way of eating. You should have a nutritionist and I highly recommend talking to that person about what your meals will look like at that stage. It might be easier to just use the meal replacement shakes for the trip then try to find food. Good luck on your weight loss journey.