In addition to my EDC pocket gear and semi-EDC waist-pack, I carry a GPS, spare batteries, piste-maps, and a little water and food.
The GPS tracks my highest speed on runs, which is kinda fun to look at, and I can preload it with maps for the areas of Europe I usually ski in. Only road maps, not topographic, so I don't know how useful it will be for navigation (because when skiing you really need to know about slopes). Normally I navigate with the piste-maps (which I don't think anyone else mentioned but surely everyone carries). My EDC will include a compass or two.
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Quality is addictive.