Yogurt would be my first answer-- just because it has everything in it: protein, carbs, some fat, and enzymes for digesting.
They have low calorie frozen yogurt as well-- just make sure it is natural (which means it might not be made into a lower calorie kind).
I believe as long as the food is natural, it is beneficial. Fruit is good, but you need something with sustenance. Maybe you can try out a few combinations of fruit with a protein source and some carbs? Or, make something sweet that is normally not (cottage cheese with splenda and cinnamon).