I am surprised nobody mentioned these
The NRS sea stow. Don't know what other names they are marketed under, but I have a few of these. A couple of them are close to 17 years old, when I started boating. Never had a leak. Used to carry my camera in one in my kayak and when I started yakking I swam a fair amount with never a worry.
Also had one that was on a raft ( not mine ) that wrapped and it was submerged for an hour or so without leaking.
What I especially like about these is the slick nylon finish slides in and out of a kayak really easily. They also go flatter than a more tubular style.
I always make sure to have a little air in the bag and a couple of rolls on the closure and you are good to go.