Small zip-lock bags with an area designed to be written on. A industrial sharpie for the label. The baggies go into an insulating and padding sleeve made from alumanized bubble-wrap held together with foil tape and this rides in coated nylon ziper pouch that I have saturated with silicone water repellant so it is pretty moisture resitant.

If I'm hiking in the rainy season, canoing of expecting to cross water I slip the nylon zipper bag into a large zip-lock to add another layer of protection.