I go to the mountains often. The first law about what to carry it's the minimum possible. If I go only for a weekend, I don't take the stove, matches, pots and pans. I'd carried prepared food from home. If you have a map and you know the nature, I think you don't need compass. (I remember one day I went to Turó de l'Home. When I arrived in the peak, there was a thig fog. I wanted change the way to return, but I was wrong. I discovered it, because the vegetation was tipycal of the south part of the mountain and I'd went to the north).
I think the indispensable thinks for to go at the mountains are:
Tent, map, rucksack, boots, sleeping bag, waterproof jacket. It's important to carry first aid kid, and perhaps a whistle.
But, there are a indispensable thinks to add: a waterbottle always full!