@AndyR SealLine has a full range of outdoor bags that I've used in sea-kayaking trips. They will keep your stuff dry. Period.
“But I reckon I got to light out for the Territory ahead of the rest, because Aunt Sally she's going to adopt me and sivilize me, and I can't stand it. I been there before.”― Mark Twain, The Adventures of Huck Finn
@AndyR This is such a great question! There are so many Options. As a sea kayaker I have used most of them! As @TomIrvine mentioned Seal Line makes a line of bags ranging from 5 to 55 liters. Sea to Summit also makes a series of bags from a tiny size of 1 liter all the way to 35 liters. The nice thing about the Sea to Summit bags is the material is a little thinner, so they weigh a little less than the Seal Line bags if they are going in a backpack.
As always with dry bags, you need to roll the top closure three times to make it waterproof, and while they are all safe in even the roughest whitewater, you will have a hard time submerging them because of the air inside the bag.
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