Wire stripping and crimping. Especially if you plan to do offgriding homesteading with solar but occasionally comes up in home applications when you want to revive a mangled extension cord or install a fixture. Specialized cables start to add up very quickly its much more cost effective to buy a big bag of connectors, a big roll of decent gauge wire, dig out an old set of wire cutters+needlenose and fire up a 2 minute instructions yt video. Like all other skills it takes time and error to get good at it but its not too terribly difficult as wel as very cool to essentially build your own electrical grid from the ground up with wires and connectors you made yourself…
About a year back I stumbled across these cool products that are a heatshrink sheath with a metal ring coated in low temp solder inside. They made all of my wire joining a million times easier. Just strip the end of two wires, push them into the sheath and blast them with a heat gun for 20 seconds until the ring contracts into a crimp and the solder flows onto the wires. Better physical and electrical connection than a crimp, with none of the futzing that comes with soldering and sheathing.
These are so cool! Do you have a link to buy?
Edit: Found them! These are crimpless solder sleeves. Crimpless Solder Sleeve Heat Shrink Variety Kit - 90 Piece