I’m learning, reading this thread, that coming from being a caver, and wilderness/cliff/high angle/ rough terrain search & rescue teams…I already have and hence automatically use all these lifechanging upgrades xD
So to add something I have not seen mentioned at all…
I really like my Gaia ap on my phone, you can predownload areas so it works as an offline gps, without needing to buy extra gear. I actually still use it even though everyone else on our team uses Garamin, because litterally I get more detail on Gaia than Garamin offers for prime dollars. For the US in particular, the pro subscription has property boundaries which has been so key in the field to know I’m not crossing lines which in back country appalachia will often get a shotgun to the face. I have lost track of the number of times IC tells me to clear an area, and I pull up the boundaries, and ask “do we have so and so’s permission, do they know we are here?” obviously the police can get permission, but as the searcher, I do not wish to scare anyone, and often they don’t know there’s a house right there in clear site of where they want searched! It really keeps everyone safe - and also helps locate local places someone may be hiding. For nature stuff, I can easily find who owns the land, and can find the correct house to ring the doorbell to get permission to walk around. So it works for both. Also having hundreds of basemap options, I can run USGS topo or various satellites or even LiDAR imagry, all which are useful in different ways. I have used it quite successfully in Spain and UK as well - obviously not all the maps are available, but there are plenty of maps and sometimes even property lines depending on the area.
Rather than worry about 'what if my phone dies it’s all on that" - I carry a little backup battery I can charge my phone about 4x with, with a cord that will run to it’s location in the pack and plug into my phone in my pack’s hip pocket where I carry the phone, so I can still seamlessly use it should I run out of battery in the field. In reality, this has never occurred because I airplane mode it so battery lasts days. (iPhone 12 mini, before that, iPhone 7). But this setup still weighs less and takes less space than carrying a phone and a garmin!
Everything else I use daily has already been mentioned (permithrin clothes or clothes made with the insect sheild; gaiters, merino wool socks & shirts - dry off well, do not smell, keep warmth in AND allow heat escape in summers literally the perfect fabric, camera with macro ability, a good LED headlamp, camelbak)
Oh I guess I havn’t seen much about first aid / safety kit - you should esp be carrying something like an Israeli Bandage and know how to use it, because gushing blood needs stopped in field instantly for any chance of survival - a lot of people bog down with huge first aid kits but the reality is you need: meds you like to use regularly (asprin, benadryl, etc), toilet paper (let’s face it, sometimes emergencies lol), large contractors type trash bag (perfect to stop hypothermia - poke hole for your head and sit encased underneath it, or it can serves as emergency poncho), whistle (because you’ll go hoarse hollering for help - I always tell folks if you hear a noise, reply with a noise!), water purification method, ways to light a fire, electrolyte replenisher, ways to stop massive blood loss, and ways to splint. Beyond that is whatever local issues you may have, but those things will keep ya alive for mostpart especially if you left a callout (where you parked - easy to check for a vehicle then, where you went, intended route, and when you will be back, with a trusted responsible person so when you should be back, they call for help fi they haven’t heard from ya). Having confidence that you’ll survive a problem is so helpful! In the US, if these simple things are done, you are basically guaranteed to be found within 24 hours. It may not be a comfy 24 hours, but it will be a perfectly survivable 24 hours.