It looks to me that "1" is just a decoupling cap to limit noise going into the op-amp which is driving the FET. (If you do the math, it filters above 30 KHz - hi-freq. Not sure of "2" though it looks to be a non-inverting integrator drive for the FET to keep the gate drive real steady. "3" is just an R-C snubber to protect the FET (R-C about 5 uS, if that is 2.2 ohms and not 2.2k).