As a 'slightly-larger-than-small' daypack, I'm disgustingly impressed with my Tenzing 2220. Good storage space, easy access to both pockets, stretchy bottle pockets, bladder port & pocket, amazing strap system, external straps that can be used for carrying extra gear or as compression straps. Expandable side zippers, either allowing you to carry a spotting scope & small tripod, or if unzipped & empty, allows the bag to expand to an extra 1/3rd it's size.
Great belt pouches too for small stuff you want close at hand.
Not cheap, but utterly bomb (& shower) proof & I doubt I'll ever find better!