Some semi-incoherent rambling on the topic: Many of the tips in this thread are great and dont involve extra "stuff", which I appreciate. I do like to plan ahead and I do appreciate redundancy where it makes sense. Especially if multiple people are carrying stuff it makes perfect sense to coordinate enough to allow redundancy. Where it's easy, lightweight, etc there is no "cost" to redundancy. At the same time, I also see people who bring 2 of everything for redundancy's sake, and in my eyes redundancy to address extremely low-odds problems with a hypothetical situation that is a low-odds occurence in the first place (i.e. the backup for your backup for when something goes wrong or a backup item that could otherwise be improvised in the unlikely event the primary is broken, etc) causes as many problems as it addresses. Easy examples, if I'm traveling with one other person I generally dont bring 2 stoves (ie a stove and a spare) to cook on, but I will almost certainly want both of us to have a way to start a fire or the stove, and I can generally tear down and rebuild my stove if needed. Depending on forecast and what we're doing I may bring a spare pair of gloves and a second insulating hat, but I am not going to bring a second rain jacket. At the same time I'd never, ever head into the mountains for more than a few hundred yards without an insulating layer and rain gear, even in the desert, having been party to more than one unplanned bivy and more than one un-forecasted thunderstorm. These may be (?) obvious, yet I see people carrying multiples on some items that seem like "a bit much" to me, while not bringing things at all that I consider "must have's". That's for them to decide, I wont stop anyone, but after a lot of cumulative time in the backcountry all over the US and around the world over the past 50 years, I also see additional safety in the mobility that comes from being unencumbered with a carefully-dialed kit that addresses 99% of the situations I might run into that can realistically be addressed, while accepting some risk for the 1% of situations that, while it is possible it's so unlikely as to be considered a one-in-a-million fluke or an act of God. To me, paring down a kit in some places and beefing it up where you feel the need for redundancy is a balance that has to be learned and is also situational. If I had 50 miles of bushwacking in coastal alaska planned, that backup rain gear might make sense. Before LED headlamps we used to bring extra bulbs in addition to extra batteries--now I'm down to just extra batteries. The first trip I did in interior Alaska, GPS tech wasnt readily available for civilian use so we were navigating by map and compass using USGS quads from the 1950's that were horrendously out of date due to the river we were on having shifted considerably during that time. Cell phones didnt exist yet and sat phones were stupid expensive, so we had no way to contact anyone under any circumstances for several weeks and that wasnt an issue becasue that's just how it was; now, it's easy to stay located and in touch with a few ounces of tech so we freak out and make contingencies to avoid being out of touch, and I guess it's so easy now that it makes sense to do that. I've also now watched multiple helcopter rescues and been first on scene for a climbing fall that required a helicopter rescue. When I was traveling to Switzerland for work I maintained a REGA membership so I could get a rescue if needed, becasue it was such an easy option that more or less doesnt (or didnt) exist where I recreate outside here in the US. Times change, my tolerance for risk and what I worry about does too I guess, although I still worry more about managing my own shitshow than I do about contacting help. I guess I should probably get an inreach since it's so easy at this point.
Also, spare snacks. When TSHTF you want backup snacks, trust me. As an old pro at this I like to keep a bag of Dots pretzels in my truck at all times. When SWMBO (She Who Must Be Obeyed) gets hangry, you, the zip code you're in, mother nature and all of humanity will thank you for your forethought. Swedish fish work too in a pinch. (a snickers bar in your oh-shit-kit can be a happy-maker)