I EDC a Mountainsmith Lumbar pack. It has a single shoulder strap but I also purchased their Strappettes which are dual shoulder straps to make it easier to carry when really loaded. Plenty large enough to carry basic necessities and still have room for lunch etc.
It fits well with the REI motif that is common around Seattle and doesn't stand out as "tactical" which I am actively trying to avoid. It also doesn't look like a laptop bag so may get less attention from thieves as well.
http://www.rei.com/product/812552/mountainsmith-daylight-waistpackhttp://www.rei.com/product/671335/mountainsmith-strapettes