Sympathy with all you fellow sufferers. It's so demoralising when nobody takes IBS seriously. It can be debilitating, but as it isn't degenerative or life-threatening most people consider it completely insignificant.
My whole adult life has been blighted by it. I have missed family events because I couldn't leave the bathroom. I've been late for work so often its affected my professional life and career progression. I've missed school events like sports day and Christmas services. It's affected my mental health, my family life and my social life. It's put strain on my marriage and friendships, and inconveniences the people around me. But it's "only IBS" so the implication is that I should just somehow ignore it.
I'm not sure that my coping strategy would help you as your reaction to food is immediate whereas my symptoms are always the following morning. But I have discovered that taking - of all things - Fybogel, makes it more manageable. I don't take it according to the instructions (twice a day, with food) because that makes things worse. Instead I take one sachet every evening after my dinner has gone down, and crucially DO NOT EAT anything after that, but drink plenty of water.
I still have to run for the toilet first thing the next day, but one trip usually clears me out so that there's nothing left for my bowel to react to. Any residual cramps and spasms generally respond to a dose of ibuprofen lysine, and any further necessity to use the loo is not as urgent.
I'm not cured by any means, but I've been doing this for about 4 months and I'd say that symptoms have improved by about 60%, and I'm no longer scared to leave the house in the mornings. I still need to know in advance where the toilets are, but I don't feel like my life is controlled by it any more.
I hope this information can be of use to someone, when the usual dietary advice has failed.