Creating a crumple texture is actually fairly easy.

1) Create new document with a white background. (File -> New).

2) Select the Blend tool and apply these settings to it:
* Mode: Difference
* Opacity: 100%
* Gradient: FG to BG (RGB)
* Shape: Linear

3) With the Blend tool, randomly click and drag in different angles and lengths on the canvas. The more varied your clicks the more realistic your texture.

That's all there is to it. Once you have a crumple texture you can do various things with it, but I'm still experimenting. I'll add to this thread as I figure out more.