I have been using a WolfPack Gear "Urban Assult" Lumbar pack for a few years. Originally I bought this pack for wildland, but it just didn't carry enough and as you can see I needed to add a CamelBak bladder to the outside. I have since moved it over to my teaching and SAR use. I like having my load low and off my back, not only does it seem to keep me cooler but it also allows another pack (like a hurting students or a medical pack).

You won't go wrong with a Mountainsmith, I have a Tour that I have had since High School and it is a nice little daypack, you can even fit a 1L bladder inside it for on the go hydration.