I bought the JOE ROCKET tank bag 2 weeks ago and I don't know how I got along without it! It has both straps and magnets, a map pocket on the top, an expandable compartment with a mesh pocket on the inside top. I carry my rainpants, chainlube, bungee net, dayplanner, wallet, checkbook, housekeys, and cellphone and its not expanded. Its got a nice handle on the end and I have been carrying it in lieu of my briefcase when not even riding my bike.
Well worth the 60 bones.