While packing for your trip, add the couscous and salt to a ziplock bag. Write the cooking instructions on the bag in permanent marker.
Before cooking, find a level area on the ground to cook on. Avoid using your stove on a raised surface (like on a picnic table), because you risk burning yourself if the pot falls off the stove.
Pour ½ cup water into your pot, and bring to a boil. Add couscous, remove pot from heat, and cover for 5 minutes. After 5 minutes, remove the lid and fluff couscous with a fork. Pour onto your plate.
Add tuna and desired amount of mayonnaise and relish to your plate, and use your fork or spoon to combine your ingredients. Serve immediately.
Notes
Note: If multiplying this recipe, follow the couscous package directions for the couscous to water ratio.