Arkel randonneur rear rack hands down! A bit pricy but well made, easy on and off, and won't mark the bike. From there you can use their rear bag or pretty much any other top mounting bag.

If you weren't touring and just wanted something light - I'd suggest a small drybag and some velcro. The smallest drybag I have will clip around the seatstays and a velco strap pulls the top against the back of the seat via the rear seat rails.

The Arkel rear trunk bag will definately handle the shoe thing, but personally I think you'd be better to look at a shoe/pedal combination that lets you leave a second pair of shoes at home.

Shimano makes several models of SPD shoes that are flexible enough to walk in - but they need to be matched with a larger platform clipless pedal for maximum performance.