My current dogwalking/bikejoring around town (and on the C&O Canal) pack of choice is an old Camelbak H.A.W.G.

I'm not using a bladder in it during the fall-winter-spring and am instead using that space for a Becker-Necker, chemical hand warmers and other items. In the outside middle expandable pocket I'm carrying a 32oz Nalgene canteen for my pup's water.

I have quite a lot of stuff in it - including MoJo bars, First Aid, the usual survival PSK stuff, Esbit pocket stove, titanium sierra cup.

I like the HAWG very much - for its durability, pockets and the carry handle on top.