I recently went to this Timbuk2 bag from a larger Topeak Wedge DryBag I originally had (wasn't too much bigger but I mainly didn't like how it sat under the seat).
I like it a lot, basically has a tube (in box), 3 tire levers, a multitool, and patch kit in it. I can stuff my big keychain into it too (gets a little tight), as well as my iPhone.