I am a long distance canoer, tough boxes the heavy duty ones) from Lowes or Wally world etc. make great boxes for loading your items.
I use waterproof bags for most of my gear and even when wet the inside items stay dry. Large military surplus ammo boxes are also good and are watertight too if the rubber seal is intact. If you load a box too full it will be awfully heavy to lift. That is why I usually go with 2-3 watertight bags and a small box, I am getting to long in the tooth to struggle with the heavy boxes, and bags.