Went to Target, and bought an upper middle price ($60) backpack. Seemed solidly built. A little larger than the usual school backpack, but lots smaller than a military Alice. Lots of pockets. Padded straps. Some Swiss company.
Holds my d5100, the 18-55 kit lens, the 55-300 kit lens, a speedlight, a box of AA rechargeable batteries, an extra Nikon battery, cleaning stuff, a flashlight, a pair of scissors for cutting vegetation, and a copy of selected pages of the PDF manual. A wad of paper towel for wiping dust off something to be shot, or wiping your face.
My wife sewed nylon straps and plastic clips, so I can mount my Promaster 7100 tripod.
A pocket on the other side holds a pint of water. So necessary in Florida, and can be used for interesting effects.
It doesn't look GQ stylish, but carries and dismounts easily, and the zipper openings are WIDE, so access is snag free. There's no intereior padding or partitions other than the laptop pocket, so my wife sewed padded sleeves for the speedlight and the kit lens.
I'm thinking of a pair of straps across the top for a sun/rain umbrella, also necessary in Florida.