The first priority would be to stay warm and dry. If it rains I would be in big trouble. Typically in such area there are no places to hide from rain. Down jacket would become almost useless when wet. Even if I had my rain jacket, it would be impossible to keep all of me dry. Would poncho be better in such case?
Personally I always have a pancho, it works as rain gear and shelter, and weighs only 10 oz. A space blanket should be included as part of your day hike or climb gear, you never know when you could be forced to spend a night or more away from you camp. A fire start kit, mine consists of some cotton balls dipped in vaseline in a old film canister, should be with you too. Some type of water purification is also part on my kit.
The next priority would be water. I hope I would be able to crawl to my pack. It could take perhaps 2 or 3 days. If the days are sunny, windless, and hot I would have to minimize sweating. Perhaps crawl at night? I could occasionally use the phone as a flashlight. If there is an obstacle I can't crawl around my situation would be dire.
Headlamp is consider one of the essentials, and should be with you any extended time you will be away from your basecamp. Also have an exit/emergency plan already planned oiut in case you get injured. Know should know where all the popular trails are relative to you location, know where and how far your nearest water source is from your intended day hikes or climbing goals for that day, before starting. Also pay attention to your terrain, memorize firewood locations along the way, so in case of an emergency, you do not have to waste precious time looking for some.
After a few days it would become apparent that SPOT didn't work. Starting with day 11, every 2 hours on the hour during waking hours I would turn on the phone for 5-10 minutes, with airplane mode off. I wouldn't keep it on all the time, in order to conserve power. I don't know whether rescuers have equipment to track cell phone signal.
Ranger and HST member George Durkee had mention that there was such newer technology, possibly military, that could be used, but he will have to clarify this.
The most vulnerable time for me seems to be when I am separated from the pack that has my rain shelter, sleeping bag, and water. There is only so much stuff that I can take with me in my pockets, hanging from my belt, and tied around my waist. It would help if I took with me the rain fly, more warm clothes, and 0.5L water bottle. What's a good way to pack that without adding much weight? A separate day pack would be too heavy. Perhaps a stuff sack with some straps sewn in? Any ideas? Another option is to have the main pack with removable hip belt and removable aluminum stays (e.g., Zimmer Packs).
Some packs have detachable top parts that can be used for daypacks, I just use my pack a Osprey 58, now a ZPack Arc, the weight is minimal, so taking it along is not big deal.
Is poncho a better emergency protection than a rain jacket?
Have used it in pretty bad weather, if the weather is really stormy it works better combine with some rain pants, but can be difficult to manage in very windy conditions, and not the best in bushwacking conditions either, so it really depends on the circumstances. A small tarp combine with some rain gear may be a better solution in some cases.