For bags I have used the Voyageur coated-nylon stowfloats with the sliding clip closure since the late 1970s. They are light, strong, and totally watertight. Several other good styles and brands are now available. Minimal weight and waterproofness should guide your choice in stowfloats. If I take a bivy bag cover for the sleeping bag, it goes in here, too, so the sleeping items are in the same load.
Many folks like to have a light tent.
If so, split the tent, fly, and poles among the users, or load it all on the paddler with the biggest boat. I prefer a tarp, because it can serve three people if well-pitched. In the other stern bag go camp clothes such as extra socks, T-shirt, underwear, windshirt, maybe camp moccasins or sandals, and whatever you may need to change into if you don't have a dry suit. Use the clothes to pad the bag, and pack so the bag will be long and slender. I usually seal the bag, suck out all the air, load it into the stern, and then let the air fill back in naturally before closing the valve.