In mountaineering, ultralight can work better in extremes because of the reduction of fatigue. There are some items which are critical, and they vary depending on the type of climb, altitude and worst possible conditions. These must allow for lower temperature extremes, and any stall in progress due to a sudden change in conditions. Poor planning, mishaps and general pilot error cause more fatalities than anything else.
Choosing clothing for weather extremes, footwear etc is critical. I invested early on in the best I could buy, with different options for different ventures and possible temperature extremes. As many errors as were made at one time or another early on, the right stuff proved it worth later on.
On lower ground, the woods etc, it has been more a matter of comfort. Again though, it depends where you are. Sudden changes in weather have killed many people at the most trifling elevations in mid summer in the temperate zones. There are plenty of choices in clothing and footwear to keep you relatively warm and dry in the worst conditions of the temperate zone. Careful choices can keep the weigh down quite well without sacrificing any safety or comfort.
