I am looking for a 100% waterproof bag for river excursions/day hikes. Must keep contents dry even if completely submersed. Recommendations appreciated!
@AndyR SealLine has a full range of outdoor bags that I've used in sea-kayaking trips. They will keep your stuff dry. Period.
@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.
Have fun!