Those newfangled synthetic wine corks make great blade covers for chisels and gouges. Colorful, too!
Use a breadboard to hold header pins straight while soldering. Insert the header pins into a breadboard and then align your circuit board on top, slot the pins through the PCB holes, and solder.
A washer with a pair of alligator clips (or small binder clips) make a pretty effective improvised workholding jig for soldering wires.
Frequent MAKE contributor Craig Smith made this ingenius puller by micro spot-welding together some nuts and bolts, to remove the gear from his cordless drill so he could replace the motor.
Use double-sided tape to secure tiny parts. You can also write the parts names, sizes, and other notes around the tape.
Need to hold round stock for drilling or thread-cutting? Repurpose an old drill chuck as a vise.