I've used these, on 5gal. and 7gal. buckets (Lowes, Home Depot), for years with no leaks in heavy rain and several canoe dumps. Haven't submerged for prolonged periods, because they float when loaded with a reasonable weight...camp lanterns & fuel, ammo, paper documents, etc. for me. The bucket handle is pretty sturdy, if you're worried about anchoring these.

If you're truly that worried that water will get in (which frankly I doubt), put the stuff in sealed heavy garbage bags inside the bucket. Protected from crushing impacts, and extra protected from water.

And I don't worry that a burglar is going to steal my stack of buckets along the garage wall: which is really a stack of shelter-in-place supplies (labeled for deception - "old paint"..."potting soil"..."fertilizer"...etc.)

https://www.uline.com/Product/Detail/S-1...mp;gclsrc=aw.ds