electron affinity and measuring open circuit voltage of insulators through rubbing
Way back in freshman physics we used Faraday's ice pail to measure charges.
You'd have to calibrate it somehow.... 

As far as the voltage (potential between the two charged objects.) that will depend on how far apart they are.  The potential will change as you move the objects about.  (This is because the charge will be constant, but as you move them the relative capacitance changes and Q = C * V.)