Sometimes what you need in life is a ginormous waterproof bag. And sometimes you need that bag to be ridiculously stout, as in military grade. That is the point at which you seek out a Watershed drybag.
Watershed makes drybags that are used by people who make their living in and around the water. Professional water guides, search and rescue and US special operations forces all trust in these made-in-the-USA bags when their lives and livelihoods depend on it. They've tested their bags to 100m deep, so chances are they're going to meet your mission profile. For all you operators out there, you can even order your bag with an inflate/purge valve if you're going to be swimming with it.
The Westwater backpack drybag is the load hauler of drybags with a 65 liter capacity. We've gone up Denali with a smaller pack, so when someone tells you you can't take it with you, show them the Westwater. It makes carrying that monster load to your raft or boat easy, with padded removable shoulder straps – sternum strap included – and a basic wide webbing hip belt. One touch we really appreciate is the grab handle, because you're always moving your load around and when you do it almost always starts from the ground, so a top handle just makes it easier.
The Westwater features Watershed's super-cool and super-effective ZipDry seal. Zip it shut like a freezer bag, and just use the attached loops to fold it into an S-curve to pull apart so you can stuff yet more gear inside. It's bombproof, like the rest of the bag, which uses top of the line hardwear and construction. Once you're all in, use the side compressions straps if you've got any room left to compress, buckle the top for giggles and you're good to go. Seriously, go anywhere. The Westwater will still be watertight when you get there.