It’s a typical contrived scenario. Your ship has foundered and as you struggle to the beach you come across a pallet of bottled water and one of diet soda (your choice of brand). They are heavy and you can only steer one towards shore.
Is there any advantage at all to grabbing the diet soda? Maybe the citric acid in Seven Up or Mountain Dew would help prevent scurvy? Does phosphoric acid do anything beneficial?
If the bottles of the diet soda are clear, and the water bottles are a brand that is colored, there’s an advantage. UV light kills the microbes that can make collecting other water sources dangerous to drink. Better penetration of UV through clear bottles can reduce the odds of getting sick if you have to rely on those other fresh water sources before rescue. (Assuming that you know to leave them out in the sunlight for an extended period before drinking.) That’s just about the packaging, not the content.
There’s some sodium, not a lot, in many diet sodas. That’s potentially got a little benefit if there’s no food available with sodium content. Of course, the typical scenario is being surrounded by salt water. Unless you are stranded on a Great Lakes island the point is pretty much moot.