Like has been said - first priority is to assess the situation. First thing in my assessment would be to determine if I could get out of the situation without having to "survive". If I've got comms, why sit in the mountains waiting for someone to realize I am not where I should be? So, I always carry a cellphone and keep it off unless it is an emergency. It doesn't weigh much and if I am lucky enough to get a signal - good for me. If I've got a map, time, and ability (energy and medically able), why sit there? If there are other (friendly) people around, why not ask for some help? There is a difference between surviving and living IMO.
I've used the magnesium starter in a blizzard in the mountains of Harriman State Park in NY because the metal on my lighters kept freezing. I put them under my arm pits to keep the warm, but that gets you cold
The magnesium starter is a pain in the ass too. I don't know why, but my buddy had a flare with him and we used that to start a fire
I start my survival gear prep at my skin. If it is going to be cold outside, I bring clothes that will keep me warm. If it is going to be hot, I bring clothes that will keep me cool. I always try to fit a change in there too. Whether it is hot or cold, being wet sucks. Cotton or wool or synthetic is another question I ask myself.
I pack for the occasion, but there are some things similar in all situations - water, food, and shelter. Always pack enough water for whatever I plan on doing and an emergency supply for what might come up. If I plan on being up there for a decent amount of time and there might be a source of water, I bring a water purifier. I usually bring iodine and salt for those true emergencies. Otherwise, there are many other ways to get water other than from standard sources. Food - depends a lot on what I am doing. If I am all out of MREs (or canned food, steaks, hot dogs, ramen, and beer) there is not much I can do other than hunt or gather. I have started to bring the Survival FM on camping trips so I can see for myself what the pictures are showing in a "safer" environment. Most basic items shelter are the ponchos and rain gear.
I didn't go over those little things, but you don't have to survive on what you have in your pocket. You might be surviving on your ruck. If I am going to have to survive, I want as much as I can. My "oh shit, my ruck is gone" survival kit is packed in a Camelbak with 2 pockets. It has a first aid kit put in to a 5.56 mag pouch with a black cross on it so others know what it is. I put a poncho or other rain gear on the outside. Water inside. There are at least 3 fire starting elements in there - lighter, waterproof matches, and magnesium fire starter with a little swiss army knife attached. I put some cotton balls covered in petroleum jelly in a prescription bottle in there. I have a daisy chained length of 550 cord (I'd say about 50'). If I am not wearing it, I put a Tikka XP headlamp in there. Also a surefire 6P or a mini-mag (no filters on either of those). I have a couple of folding knives I put in there, but they change depending on what I feel like pulling out at the time. I also put something(s) reflective in there like a reflective belt and/or a mirror. Reflective belt is really smart when you are walking around in the dark on a ruck and you are looking for your buddies. I put a pen and a notebook in there. I also put communication equipment in there (cellphone or handheld 2-way). Depending on the climate, depends on the type of gloves but I can't remember ever not having gloves in there. That is all off the top of my head from what I usually use. It changes depending on where I am going and what I am doing, but I think I got the basics.