I've got a small Deuter backpack. It's actually the daypack that pops off of this bad boy: http://www.amazon.com/Deuter-Quantum.../dp/B001QTRCUU
It's perfect for quick day rides where I want to carry a lock and tools/pump + a pair of shoes or some discs for disc golf, etc. Probably use that the most.

Also got a Camelbak Mule, which I don't bother using the bladder with. Makes for a pretty versatile all-around backpack. About twice the capacity of the Deuter.

And the messenger bag, for when I need to haul lots of stuff, or bigger items, or I want to look cool. Custom black/green/yellow, made by some guy.