Slippery Elm (bark) is a wonderful, mild all-round remedy. It's great for constipation and diarrhea, for respiratory conditions and indigestion, etc. (See below for more info) It comes in a powder form, has a pleasant smell (like icecream cones!) and tastes slightly sweet. Be sure to buy organic.
If you want to turn a fruit smoothie into a firm dessert, add a little Slippery Elm to the mixture in the blender.