What kind of brakes?
For derailleurs I just pull the cable snug with my fingers or a needle nose plier. Honestly, I suspect it's more important to get the cable housings snugly seated in the frame stops than to worry about cable stretch.
For brakes it depends a lot on what kind of brakes you have. Calipers and V-style brakes I just use my fingers. Newer style canty's too. Older style canty's can be interesting.
The most challenging are freestyle BMX bikes with under the chain stay brakes. Those sometimes require my 3rd hand tool, my 4th hand tool, and the use of words that are not permitted to be uttered on US Navy ships.
My 4th hand I mostly just use for pulling cable ties.
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My greatest fear is all of my kids standing around my coffin and talking about "how sensible" dad was.