A simple, inexpensive solution is the "Voice Activated Lightstand" or VAL. The VAL is a joke term for an assistant holding an off-camera light. Here is one example of a small, easy to carry, VAL kit:
This kit consists of 4 pieces:
And of course a Nikon Speedlight. In this example, I'm using an SB-800.
This kit assembles in seconds, and provides a small, portable lightsource:
And it produces a nice, soft light that is easily movable, assuming you have a cooperative assistant!
You could also use a small lightbox with the flash in much the same manner. But the shoot through umbrella provides a nice, broad lightsource that is pretty quick to setup.
And you get a monopod to use with your camera as a bonus!