New from Outdoor Research are these waterproof dry bags and packs made. Copy below mostly from OR, with a few editorial tweaks.
The DryComp Ridge Sack (above) is an ultralight and waterproof day sack with all the features needed for big mountain bike days, whether your climbing or chairlifting to the top. Radio frequency welded seams and reinforced fabric on the bottom and pocket area provide maximum strength and waterproofness. A mesh pocket accommodates a hydration bladder and stretch cording and gear loops secure shin guards, body armor, etc. Compression straps cinch your load down and breathable mesh shoulder straps combine to offer a comfortable fit while riding.
+ Ultralight, waterproof 70D nylon fabric
+ 420D nylon fabric for durable, reinforcement on bottom and around pocket
+ Radio frequency welded seams for highly durable waterproof seals
+ Roll-top waterproof closure; durable buckle secures roll top
+ Mesh back pocket with elastic stretch cording secures loose items and doubles as hydration sleeve
+ Two compression straps
+ Spacermesh shoulder straps are supportive and breathable
+ Dual ice axe loops with shockcord ice axe keepers
+ Dimensions – Rolled: 24″ x 11″ x 8″ / 61cm x 28cm x 20cm
+ Volume: 2075 cu. in / 34 L
+ Avg. Weight (oz./g):  16.4 / 465
+ $119
Lateral Dry Bags
Our most rugged dry bags have seams that are radio frequency welded for maximum strength and waterproofness. The roll-top closure ensures the waterproof seal. With a clear window that runs lengthwise across the bag, being able to view the bags contents in a deluge is key to finding the one piece of gear you want without getting everything else wet. The horizontal construction enables you to find gear more easily with a wider opening and a more shallow depth. Compression straps, two on the ends and two around the body, cinch bulky loads down small.
Size: 15L: $49
Size: 45L: $69
Size: 10L: $39
Size: 25L: $59
Graphic Dry Sacks
Store your socks, sleeping bag, or down jacket in these durable dry sacks. The fully seam taped, coated nylon ensures protection if your gear takes an unexpected tumble into the water. Unique graphic designs help with quick organization and gear finding.
Size: 10L Skyline: $15
Size: 25L Wave: $18
Size: 5L Zig Zag: $13.50
Size: 10L Fern: $15
Size: 15L Clouds: $16
Size: 15L Bubble: $16
Size: 25L Barn: $18