Do you have a MEC nearby? They've got some nifty things, like a pannier that turns into a backpack (if you're willing to buy a new one). You can also get both pannier and shoe rain-covers, though that's adding to the "stuff".
Also, maybe check out the Merrel "glove" shoes. They're like the five fingers without the toes, so they look like normal shoes, but they're equally foldable. I can even shove mine into my (woman) purse, though it helps that I've got tiny feet. They're also the most comfortable shoes I own and I wear them all the time.