This is a very useful device. Very simple in concept and so practical. It is the same width as an iPad but about an inch longer so you could fit it in a pocket suitable for an iPad. As other reviewers have mentioned it is great for small items that you need to carry, especially computer parts, but it works just as well for small camera parts and cables, even rolls of film or memory cards. In fact you can put a multitude of things in it, the only limitation is your imagination.
On the back there is a loop so that you can hang it from a hook if necessary, and a clever expandable pocket that opens up when you unzip it. This covers most of the back so you can get lots of very small items in there. After you fill it up your next question will be what else could benefit from having one?