Nearly instant spring-loaded pliers. Remove spring from back of an old bath fan cover, cut off the end hooks and insert ends between steel handles and cushion grips. Been using it at work for 15+ years.
For hard grips, use a spent pistol recoil spring and a length of surgical tubing. Lube the spring and tube interior with Ballistol and struggle for 20 minutes while questioning your life choices and squeezing the spring into the tubing. Add more lube to the tube and to the handles and slide the tubing on.
Uglier than a baboon's buttocks, yet functional for years until the tubing wears out.
Custom on-board high-power rare earth magnetic screw bit holder for drill/driver. Also holds drill bits and small screws during repairs.
I've been using this at work since I concocted it probably 17 years ago. Use a large ring magnet (really a cylinder with a screw hole thru the axis) from K&J Magnetics. Large washer on bottom acts as shelf for bits but also guides the magnetic field thru the bits and into the top washer utilizing both poles for much more strength. Head of machine screw holding entire assembly together is just inside back of the drill. This requires disassembling drill and Dremelling a hole for the screw to exit. This voids the warranty (See what I did there?
), but I go thru drills so fast they'd declare it abuse anyway. This gadget is so tough I think I've only rebuilt it once or twice not counting reinstalling it on new drills.
And finally.... Rain puddle. Good for cleaning boots.