If you live near the ocean, you can create an incredibly valuable resource. There are several methods of producing salt from seawater. The most primitive is to sand down smooth sticks, char the exterior, then plunge the hot sticks into the water and pull them out quickly. Salt will crystallize on the exterior as the water evaporates. Brush the salt and ash into a collecting bag and keep heating and plunging.
You can also use any shallow clear plastic container as an evaporative salt mine. Simply pour a small amount of sea water (no more than 1/8 to ¼ inch) into the bottom of your clear plastic container and leave it out in the sun to evaporate. The shallower and wider the container, the faster it goes. Clear plastic tote lids are a good choice due to their size and depth.