Oooooh, so many choices.
Do you have a particular look or style you prefer?
I use a couple of different bags depending what I'm hauling that day. My basic loadout is a netbook and accessories, notebook, whatever book I'm reading, a light duty Firstaid kit pens/pencils, glasses, pocketmod
set up as planners and some water.
For smaller duty and what I use the most around town or light day trips is a Mountainsmith Day
lumbar bag. These can be found at many stores but better prices online usually. A good shoulder strap (my primary carry), waist belt which tucks away nicely and handles for short hauls. Mountainsmith sells a "strapette" that converts it into a backpack. I own and like the strapette, but I don't use it much.
In a larger size but more messenger bag style, Timbuk2 is a popular and quality brand. You can customize colors and more on the website to get what want.
My next step up in size is fishing backpack from Fishpond. I have the Double Haul
. And while it can take some sizeable books, that's not it's best use. For that you'd be better off with the Shooting Star
if you like this particular design. These are pricey but I love mine.
For larger tasks, the Jansport Odyssey
is my pick. But mine mostly sits idle until I travel. The current version of this bag is different from mine. They change the strap padding every year and move pockets around but the primary features are fairly consistent.
These are all fairly streamlined civilian outdoors bags. If you like other styles, there's lots more too choose from. edcforums.com - Index
has a forum devoted to bags for everyday use in all size and price ranges. They have a bit of a military fetish which are also good bags but other kinds too.