Dry box

Commonly called Peli-Boxes after the company that makes some really good ones. Peli-Boxes, or Pelican boxes are a brand name - like Xerox.

Dry boxes are rigid containers that are watertight. They are also airtight. For that reason, the good ones have an air valve that can be opened to allow air in or out if atmospheric pressure changes from the time you last closed it til you want to open it. Some have automatic air valves - in my limited experience, these actually work. Some dry boxes are sold with precut foam inside; you can pluck out bits of foam to custom fit the liner to whatever you want to put inside.

Cameras, electronic widgets and other expensive stuff deserve a good dry box. Available in many sizes from less than a liter to many liters in volume. Prices vary according to size and quality.