I have found that when I take a handlebar bag I actually prefer to remove all of the original mounting hardware and use the little front rack sold by nashbar or under the sunlite brand. If I remember correctly it weighs about 12 ounces. I used it with a Nashbar Elite bag and was pretty happy with it. I wrapped the shoulder strap in a kind of figure eight on the stem and the bag stayed put pretty well. I took some of the stiffening out of the bag to save weight since it didn't need it as much when sitting on a rack. The rack and bag wound up weighing less than the standard bag and mounting hardware.
It is intended to mount on the canti brake bosses, but I have adapted it to a p-clamp setup before as well, by using a little aluminum plate on each fork leg with double p-clamps.
On some trips I have used a bar roll instead and on a couple trips hung a little Mountain Hardwear camera bag on it.