Jseis 

I have "sensitive stomach syndrome" which is more less like IBS so I've learned to go mild which means sips of water, not downing lots of sports drinks at once. Fried eggs & white bread...no grease...maybe a tad of butter, or my fav...white bread, turkey bologna and a little peanut butter & honey. Flour tortillas & a few beans, rice, chicken. Everything in moderation. I stay way from energy bars as they can kill my stomach. I've read where the one thing that pro bikers fear is stomach upset as it can ruin your day completely and I believe it. Protein really helps stabilize my stomach but I can't eat a lot of it at once while riding. I'm not a racer. I like longer rides so I eat a little bit all the time. That being said, exercise is the best thing for calming my stomach and I practice with various food types just so there are no surprises.