The Topeak Alien II has over 26 tools in a 1/2 pound package that fits in a nylon case that can fit on your belt - or in a small seat-pack. It is designed specifically for bicycles. I love mine! I have a almost complete shop at home, but this is what I carry.
http://www.amazon.com/Topeak-Alien-2.../dp/B000FIE4AE
I believe this matches your criteria for one that will do most everything. It will. Including chain-tool and spoke-wrench.