I'm always on the lookout for the perfect bag, and have never found it. I would be interested in what you come up with.
One thing that makes my life easier is that I'm using an Asus EEE-PC, which is small and light, and uses a solid-state flash drive instead of a spinning magnetic hard disk drive. I carry it in a small case sold for portable DVD players. With the power cable and everything else, it weighs about a kilogram. I'll never buy another full-size laptop. For a helmet bag, I'm using a FSI bag they give away to hold the 1/4 ton of books they supply for the S76 course. It's not padded, but it's relatively strong, and I have no other use for it, plus I'm too cheap to buy a dedicated helmet bag.
