Dry Duck Marine Grade Waterproof Dry Bag

https://www.amazon.com/dp/B01JA8BLXC

This is an excellent quality dry bag that I received at a discount in exchange for my unbiased review.

The material it is made from is waterproof, rubbery, and double-layered. 

The bag seals by simply rolling the top down over itself a couple of times, and then attaching the two ends with clasps. There is also an adjustable shoulder strap.

One convenient addition is an outer pocket that is probably at least somewhat, if not completely, waterproof where you can store things that don't need to be kept totally dry, like keys (not electronic keys), laminated IDs, etc.

I am very pleased with this dry bag.