Full set of conductive rubber for Nintendo 64 controller. These rubber pads go under the buttons. 
You may choose between:
- Used OEM (official) rubber pads
- New aftermarket rubber pads

If your controller is dropping inputs, it might be due to worn conductive rubber pads, in this case I'd recommend getting a new set. The aftermarket rubbers are surprisingly good, their main difference being that the face buttons (ABC) are slightly firmer to press.  If you believe this will bother you, then consider getting a used OEM set; I've thoroughly tested them but have a very limited supply available.