Another option would be a "top-tube" bag...also referred to as a "bento box" amongst the triathlon crowd. They come in various sizes (I have a medium-sized one by RAV-X on my bike) and colors. They have velcro straps that attach around the top tube and handlebar post. In mine I usually carry a lip balm, cellphone, an energy bar (like Clif or Luna), and a pack of gummy chews (like Luna Moons or Honey Stingers). I've also squeezed more stuff in there when I've needed to.

This is the one I have, in medium:

http://www.ravx.com/2010_product_pages/bags/to_go.html