I'm always solo, so at minimum (in order priority), I always carry a knife, food / water, an IFAK, 550 cord, magnesium fire stick, space blanket, bandanas, PLB / sat messenger, rangefinder, flashlight (with a backup windable / dynamo type), headlamp, PVS-14, lens cleaning tissue, and a lightweight padded hunting mat. Also clothing layers for the worst possible weather in the area that I'm in (including microspikes for ice) and a sidearm for protection.
If I'm out really deep in the mountains, I'll bring a good "bushcraft" tarp, extra cordage, and a bivvy sack. I've broken a leg once already and I'm often in areas where I can't get satellite reception in weird canyons / valleys with thick canopy. The idea of hypothermia with a broken limb makes the extra weight worthwhile.