I'd buy a few iPhone SEs as spares. In a similar vein, I currently use an iPod Shuffle on runs and hikes, because it's cheap, light, and durable. They retailed for $50 from Apple, and now that they're discontinued, they seem to be selling for $80+ on Amazon. I wish I had invested in a stockpile, so I could sell most at a profit, and keep a few for personal use.