Personally, my symptoms if I eat something that doesn't agree with me (or eat too fast or don't chew well enough) are stomach pain/cramps, nausea, lightheadedness, fatigue, and sometimes a racing heart. Often, I have a feeling like the food or fluid is sitting above my stomach and taking some time to get there, though this particular feeling has been fading away as I progress.
I have never, not once, actually vomited - not even close. (Which I count myself lucky for.) I also seem to have a reaction pretty quick if I'm going to have one at all, which also seems like a good thing.
I am 5 weeks post-op, and I often feel tired and lightheaded after I eat even if there is no pain or nausea. Not always, but usually. I try to plan 20 minutes to lie down after I eat. I'm hoping this symptom goes away someday, or else I'll never be able to eat out!