In an emergency, it's entirely likely that a blade will be grossly abused and need first aid on the spot. It's best to have a plan for that.

I have been using industrial diamond paddles/plates for the last decade or more, and for practically all repair work. They are lightweight and they cut fast. My old style stones, while awesome, gather dust.

EZLap and DMT are the best in terms of longevity. I have been also using PRC diamond paddles/plates which work very well but wear out quickly. In an emergency kit, any of these would be highly useful. This is what I carry when I travel; you just have to assure airport security that "it's an abrasive, like sandpaper."

One other tool that makes it into my travel/car kits is a specialty submicron 100 carbide scraper. Sounds barbaric, and it is, but a tiny slab shapes a lot of steel. It has proven its worth though the ultimate edge is crude. There are brands like Speedy Sharp, also Corona sells them for sharpening pruners/loppers, and I have seen generic versions also.