Here are two waterproof boat boxes to store emergency gear and regular gear. Boat boxes are good for protecting crushable gear from tsunamis or your stupid feet. I love flexible waterproof bags and have several, but for the delicate expensive stuff, the box works for me. The photo shows the gear that goes in the large box, minus a flashlight, because I am between flashlights and am seeking a good bright LED one I can afford.
Design Worldview comments:
(1) Bags are good, but Boxes are more Multifunctional -- Boxes can double as hasty stools. I love multifunctionality. Modification: either box could incorprate a small closed-cell foam pad, with nylon cover, to make these boxes into gear-and-tired-butt boxes (not to mention add flotation power).
(2) Weight and Buoyancy -- These boxes are rather heavy (big one is pine, epoxy coatings in and out, fiberglas cloth as abrasion protection, then paint. However, the weight is mostly from thick wood, which floats. You can build them lighter without sacrificing much strength. Thus, the small box is marine plywood on four sides epoxied to pine squares at the ends, so it is lighter.
Closed cell foam used to pad the interior also provides floatation. The boxes float when sealed, but what if you capsize right after you open them? Well, good luck! You can't design around all the issues. More closed-cell foam to insure flotation (the boxes hold some heavy stuff after all, such as tool kit, radio, and flashlight); more foam means less carrying space inside, means larger box needed, and then what? Write a treatise entitled, "The Engineering Trade-off as Analogy for the Human Dilemma."
(3) Interior design -- the large box has a partially-dedicated compartmentalization to separate one-time use gear such as flares, flare-gun, light-sticks, from hardware such as radio, light, tool kit. The concept is that you want to be able to plunge your hand inside and snap up exactly what you need for type I emergencies ("Help!") and type II emergencies/issues ("Oh, damn it all.").
(4) Now Decide How Many Boxes You Need -- "And why do you have two boxes?" Because....epics are fine, but every day on the water need not promise Green Giants, scylla, and other events worthy of entry to the Explorer's Club. For those days, and those boats, an option for a small box is good. I may be wrong, but I think all the flares, radio, tool kit, etc., are a bit of overkill for kayaking a few hours in the local river-swamp.
(Marginalia for the Positively Pedantic -- Note the saw, which I made from a replacement sabre-saw blade with handle wrapped in epoxy-soaked nylon cord. Why? I could find the size that suited me, and make it cheaply since tools are known to rust and be lost. Why carry a small saw? Because you never know.... Other tools are a Leatherman and a hand drill, and in fact have needed both for repairs, once. Sheaths for saw and drill made from polytarp and ductape, loose fitting and stiff to allow aeration.)