Kit that earns its weight
Every gram on your back is a gram you carry up. After a few soakings you learn what actually earns its place.
Map and compass before phone — batteries die in the cold and a paper map does not lose signal. Two pairs of gloves, because the first pair is always wet by the summit. Something hot in a flask; it is morale as much as calories. And a whistle, which weighs nothing and matters once.
The thing I leave behind now: spare gadgets. One head-torch, checked, is worth three you never test.