To me, no pedals are essential. The pedals I find most useful are probably a fuzz and an octave pedal.

Compressor pedals encompass a pretty big variety of pedals and many of them have features beyond just compression like tone shaping and sustain control. A pure compressor is going to have a pretty subtle effect for controlling frequency levels and not really essential, especially playing live, especially if you are just starting out, where you get more benefit from just learning to control your sound with technique.