I'm working through physical therapy after my second shoulder surgery. In my commuter kit, I've dumped:

• all snacks
• umbrella
• dropped from a 1L Nalgene to a 500ml bottle of water
• a few infrequently-used tools
• downsized my primary laptop bag flashlight
• paper notepad in exchange for iPad
• spare mouse

In all it's about 3-4 pounds down from where it was. For all that my bag is really heavy compared to most. Much of that weight is in tools that I really can't part with. The things I carry strictly for emergencies make up only about one pound of the load.