I have IBS with constipation, and I've been dealing with it for about 17 years. I also have a congenital kink in my colon which makes everything even more fun.
What helps me is a very high fiber breakfast and lots of water during the day. I also snack on fibrous foods like apples, prunes, raw veggies, wasa crackers, etc...
Anything high in fat or sugar nearly kills me. I will have severe cramping for days. Chocolate in moderation doesn't bother me, but any type of candy is off limits for me.
I have one drug called Buscopan (smooth muscle relaxer) on hand for severe flare ups, but I rarely use it. Fiber and water seem to do the trick.