A messenger bag is easily adjustable for load, one strap and a big buckle.
Easier to load as it is wider, easier to find stuff in and will crush you lunch less, Thermos will fit crossways. Mess bag is stylish on the job site and around town. You will look and feel like a bicyclist, not a hiker. I am using a Timbuk2 bag.
It's really nice.

http://www.timbuk2.com/tb2/products/messenger/

Here's a medium for $54
Made in America

http://www.rei.com/product/782784

Lots of options here

http://www.amazon.com/Timbuk2-Classi...2416377&sr=1-2

Bill