I carry everything I need in a large seatbag. Seriously, it sounds like you are carrying a lot of stuff you don't need. Think like a backpacker -- everything that is not necessary stays home. I keep a pair of shoes in my office as well as a supply of clothes and food, which I restock on days that I drive.

The two photos attached show my seatbags. My large bag is the Carradice Barley, but most of the time I use the Acorn bag that holds about half as much gear.