I just bought an Osprey Karve 16-liter for the exact same purpose. It is somewhat lacking in smaller pockets, but it holds every I need quite nicely, and is rugged and waterproof, since it is ultimately intended as an inbound/sidecountry day pack for skiing. I love it, and never leave the house without it anymore. Plus, their unlimited lifetime warranty is top notch. repairs/replacement for life.
Check it out!