"What tool(s) or machinery make you more self sufficient?"
It's been very rare that I've bought any tool or piece of equipment that has been used once and then has sat for five years, or something like that. Meaning I've tried to limit my acquisition of tools to ones I use. And all of them make me more self-sufficient... in that, because I have them and have learned to use them, I save money, and/or save time, and don't have to call on the assistance of others (including professionals) so much.
Around here, neighbors do borrow tools or equipment from one another sometimes. But there's a sort of rule of thumb or maxim that a lot of us subscribe to - "if I have to borrow it three times from someone, maybe I should buy one for myself."
I could cite my pickup truck as very important. I could cite my chainsaw, rototiller, and mower as some motorized tools I rely on a lot. I've got hand tools (bow saw, shovels and spades, garden fork, scythe) that can do essentially the same tasks, but the motorized ones save me time and help save my energy for other tasks. I've got hundreds of small hand tools (sockets for my wrench set, pliers, screwdrivers, wire cutters, vise grips, etc) - and collectively, I'm drawing on these virtually every week of the year. And during the fair-weather season, I use some selection of them pretty well every day. I could say something similar for my carpentry tools.
I like having my equipment to do welding, brazing, and heat forming. If I didn't have it, I'd be begging or paying someone in the neighborhood to do certain essential tasks for me.
And where would I be without my snow scoops and shovels for the wintertime?
So, the original question is not an easy one.
