I carry this backpack everyday to work instead of a purse.  It holds my 16oz nalgene in one of the side mesh pockets and a similar sized bottle of iced tea in the other side mesh pocket.  The small zipper pocket fits my small wallet, ipod touch, and some other small items.  The large compartment fits my lunch (if I choose not to carry a separate lunch cooler), gloves, hat, and other small items.

I also use this backpack for good weather, half day, less than 5 miles round trip hikes.  For that I can fit a 16oz nalgene in each mesh pocket, a 1L playtpus in the internal sleeve, lunch, a rain coat, and first aid kit.  I have removed the "hip belt" as I find it getting in the way for my purposes.  I would find the hip belt useful for bike riding or climbing.  One thing to note is that the exit port for your hydration bladder tube is only over the right shoulder so if you are dead set on having it over your left shoulder this might not be the pack for you.  I love how the tapered design and simple frame make it feel like I have nothing on my back.

I chose this pack over the 10L and 20L versions of this pack because the 10L would be a tight squeeze for a rain coat and lunch and the 20L had compression straps that I feared would get in the way of the side mesh pockets and I just didn't need them.