Few days ago we went to the cinema and our kid asked for Pringles. I asked him to keep the can when he finish and took it home. Here's the can:
Also we need a black scotch tape, scissors and ruler. Measure your off-camera flash's head. My Canon SpeedLite 550EX head is approx. 75x45mm. Grab your can, draw marks and make 40-50mm cuts. Put it on flash head and use scotch tape to fix the new form. Of course, you can cover all the can carefully with black scotch tape and make it look a bit better. I left it like this. Congrats, you are done! Here is how it looks on flash:
Here's the result of this light modifier (click for large photo):
It was shot at home with enough ambient light and HSS (High Speed Sync) on. The surroundings are totally dark. Flash was on camera, light comes from the above of the model.