How can I quickly and safely discharge a charged capacitor (small and low voltage; <= 42V)?
With small capacitors up to 1 mF, there is little to worry about.  I suppose it's a good idea to make sure they are discharged before plugging them in where the voltage that could be on the cap could damage something, but this is something not generally worried about until you get to some real energies or high voltages.

For small electrolytic caps like what you are working with, just short them against something metal, like a bare component lead, metal chassis, or handy screw driver.

Don't waste brain cycles thinking about this for anything small enough to be a ceramic cap you can plug into a breadboard.  By the time you plug it in, your fingers will have discharged it.  Even if not, do the math.  1 &micro;F at 10 V is only 50 &micro;J.  Yes microJoules.  Big deal.