Seconding the Canadog
The entire kit is a little more on the pricey side; but I really like the features it comes with.
There is a pocket on the side that's big enough to fit both my phone (Nexus 5 in a case) and keys without being too bulky. The thick lined back helps for maintaining better posture and has a water bottle holder. And it's just super comfortable.
There's lots of different rings to attach dogs to depending on where you prefer to have them, or for walking multiples.
The only thing I'm not 100% thrilled with is the size. I keep mine as tight as it goes and it still feels a little too loose on me (and I don't consider myself to be a supremely thin person at all).