I have been doing more and more multidays over the past few years. The biggest thing I learned was to buck up and buy some lightweight, kick-ass food. Mary Jane's Farm Organics has incredible food in bulk(re: less trash). The potatoes w/cheese and baco bits are great as is the chili mac among others. We bring blocks of excellent cheese, high end jerky, good coffee/cocoa, Probars etc., and plenty of good chocolate(I recommend a mix of the Endangered Species Bars. Organic, high cocoa content, great variety)
The difference in cost versus the old ghetto ramen noodle style we used to roll with is about $25-30 per man for a three day trip. The reward is immeasureable. No more going hungry or wishing for this or that. The difference in weight is a coupla pounds and makes a nice counterweight in your bow. Just put the last day or two of grub up there and leave her be. Less tail stands for sure.
I am a firm believer in ultralight, but not at the expense of a good time. And believe me, I have had it both ways...
Futa bags are the way to go on the drybags. Mine have lasted six seasons of abuse without one leak.
Black Diamond Megamid has slept five on several occassions with the OR bivys on the outside. Excellent tarp, light and durable. You can string it between two trees or use driftwood for poles.
I like a Bivy sack with the tarp, preferably one that I can puff in and zip up tight. "Bag hits" are a great way to end the day and are the gateway to a long night of semi-lucid bearanoia...
Oh yeah, if you like booze, bring some. If you like herb, bring plenty, if you like tobacco, bring tons. The one thing I have really learned on the trips is that the extra few pounds only adds about 1-2% to the weight of your entire paddling set-up(you included) on the water. The difference between my old bare bones style and the recent voyages aboard the New Love Boat in the hard class V is about nil. If that tiny bit of extra sluggishness is gonna make you wreck, Captain Stubing should probably reconsider running that drop in the backcountry anyway. Another option that we have employed is to stop at the head of a tough stretch(if reasonable in length) and portage our gear downstream 'til it mellows. This allows for a good scout that day and a second look on the hike back to the boats in the morning. If its good to go, your light as a feather. If it is too much, your load is lighter... For some trips, this method may add a day or two. But that is a day or two out in the wilderness. Our biggest mistake on multidays has been not slowing down even further and relishing those fleeting moments of sweetness way back in somewhere immersed in the Big Secret. Hope this helps. Have fun out there.