
When I do use a flash, I use a white card secured on my flash with an elastic band, and this works reasonably well most of the time...but perhaps the Origami will do better?
The Origami is a diffuser that can be swung into the flash's light path, and is foldable (hence the name), taking virtually no space in one's bag or even pocket. Although I rely on natural light as much as possible, I think I'll order one and see if it lives to its hype. It's currently on sale for $30.
Gary Fong's Origami