How can I transfer pictures from a USB flash drive with the Camera Connection Kit?
This can be done by imitating the folder structure of a camera's memory card.

First, find a flash drive that's compatible with the Camera Connection Kit (i.e. doesn't draw more than 100 mA). 

Create a directory in the root of the USB drive named DCIM. Inside DCIM create a directory that has exactly 8 characters. Put your picture/video files inside this directory, ensuring that they have an 8.3 pattern filename (e.g. somepics.jpg). 

You'll end up with a directory structure that looks like this:


USB drive root
  -\DCIM
    -\FAKECAM1
      -\pict0001.jpg
      -\pict0002.jpg
...