My 'essential' list would include.
Heavy gauge extension cords, gloves (for handling hot lights), 4'x8' white & black foamcore or 2 black & 2 white dropsheets, 4 gripstands with clamps, 2 blonde lamps (better yet, the newer Kinoflows Flouresc. or LED lights) Spare bulbs, gaffer (duct) & black tape, hd clamps, stepladder...
(I'll add to this if I think of more - there likely is)