I have had the RnY surgery. At that point in your journey, you'll be on regular foods and should have made enough mistakes to know how your new body can eat. Do yourself a favor, though.... do NOT keep doing things is does NOT like to train it to eat the crap that got you to the surgery in the first place. Remember the old adage "My eyes are bigger than my stomach"? oh so VERY true! You can ALWAYS ask for more if you are still hungry, or leave the dining room and hit the buffet. But if you are honest with yourself, you wont be hungry. Food is loud. Just be certain to acknowledge the discomfort in your small, overstretched stomach is louder..... I hope this helped!!
(ps, lost 60 lbs with surgery, gained 20 because I didn't follow my own advice, lost 40 & maintained for 3 years)