Eating more fiber can help keep your bowels regular. One kind of fiber, the "soluble" type, is especially helpful for opioid constipation. You can get it in foods that get soft when you add water to them, like oatmeal, barley, and flax. You can also get fiber from fruits (especially prunes and even warm prune juice), vegetables, whole grains, seeds, and nuts.
Don't use fiber products that have psyllium. They can make opioid constipation worse.