My setup is: a Mountain Hardwear 40 Lamma synthetic (packs pretty small and is light) bag with a compression stuffsack, sometimes a bivy sack, a Big Agnes insulated air pad 3/4 length (super light and super small) a GoLite Shangri La 3 (pretty light, pretty spacious, and packs to about a football size, and Watershed stow float. I also wear fleece pants and a synthetic pullover (Puffball) for campwear and to sleep in as well.
I think its almost inevitable that your sleeping will get at least a little wet, weather from packing it in and out of the kayak, or condensation, or any number of other things. Therefore, i stay away from down bags. Others pull it off though...