I guess it can all be boiled own to this.
If you want the most convenient and smallest thing possible, you're best off with a small chest pack.
If you want a pack that will hold lots of gear, has lots of features, and not shift around too much, you're best off with one of the better chest packs out there.
You want something more traditional that will hold plenty of stuff and will add some warmth, there are lots of vests out there that will serve you well.
You want a vest that will hold everything and the kitchen sink, ride well, and do well in all weather, you're into expensive vest territory there.
You want the coolest (meaning temperature comfort) thing possible that will hold plenty, I think a fanny/waist/hip/belt pack is the way to go.
Cooler still but with less stuff, a lanyard.
And if you want a pack that will give you the option of either a good chest pack or a front-and-back pack that will carry alot of gear (rainjacket, extra fleece, lunch, whatever) the Fishpond pack that www.thefullcreel.com
carries will likely be hard to beat.