Lately I have been using a small sling-type bag more and more. I
wanted a bag that was smaller than my large Courierware bag for when I
wasn't carrying my computer. I got a very small bag that held all my
gadgets but then I always ended up carrying a book in my hands. The
sling is large enough to carry my gizmos and a book, but not my
computer or, say, an 8X11 rigid item.
If anyone does want a bag that will fit a laptop, Courierware bags
(http://www.courierwareusa.com) are amazing. Indestructable, water
resistant, and you can select for more or fewer pockets. You can throw
the whole bag in your washing machine. Great for everyday use *and*
bike commuting. They also have a series of scaled-down "walking bags"
but I suspect these may be still a bit large for what you're looking
for. But maybe not.
http://www.ebags.com/mountainsmith/day_pack/product_detail/index.cfm?modelid=3148
hmm.... perhaps I've been too hasty in ruling out the fatboy. Although, since I'm a pretty big guy (6'2"/250lb.) most people don't mess with me anyway. :) There have been a couple occasions when I've slipped my boning knife into my jacket sleeve. (with a blade guard) That was last fall (on a train that runs near the state fair) at about 10:45pm.