Emergency shelters - what works/what's practical?

In the light of several incidents we have been discussing, what do people carry, what would be their ideal emergency shelter? I'm thinking of a scenario similar to that Bennington and Jackson faced, on the tops, unable to continue, windy and snowing / near snowing. Both for overnight trips where aim is a hut and for daytrips. Some will say carry a good alpine tent and a sleeping bag even on a daytrip just in case, but in reality most are not going to carry that much when going to a hut or on a daytrip. Some thoughts: Two survival bags with your sleeping bag would be cheap, light and bombproof. Stuff sleeping bag in one survival bag, stuff other survival bag in sleeping bag and climb in boots and all if necessary. Down sleeping bag should stay dry even in a damp hollow between the tussocks when its howling and sleeting, Inner survival bag will keep your damp clothing and eventual sweat from wetting out the down bag that most of us carry. Saves that messing around trying to get damp clothing off before getting into the sleeping bag, saves losing gear you might need the next morning, given your mental and physical coordination is probably shot at that point. Breathable Bivi bags - either the SOL aluminised ones or various other waterproof breathable bags. Probably good, more expensive, heavier, but have some use in non emergency situations. Down sleeping bag will probably lose insulation overnight as it gets damp from wet clothing and body moisture and moisture seeping in from outside once the outside bivi bag is completely wetted out. Again, a second mylar survival bag on the inside of the sleeping bag would probably make a big difference keeping moisture away from the down. I tend to go with the top option when going to a hut in the winter. In other situations (aiming for valley camp following tops travel) I have a light bivi bag plus very light polycryo tarp with lots of guy points all around it. I could use the guy points to tie it into a bag and crawl in in an emergency on the tops. Carry a mylar survival bag as well to use as a vapour barrier in an emergency. Other thoughts: Systems that let you conserve heat of 2 or more people together - bothy bags and similar? Big advantages if you can huddle together, more of a problem if people are separated or one has to go for help. Day trips when you aren't carrying a sleeping bag? The Czech woman on the Routeburn did well to survive three nights out on the tops in the midwinter snow and still make it to the hut after they got in trouble, she must have had some combination of good gear / strategy / toughness to get through that. Who's had to hunker down in a real emergency situation / spent a night out with only emergency gear?