Originally posted by Digitalis Agreed, and readily accessible spares too.
Yep, it does no good if they're out in the car park or back at the home office. And little things will kill you - AA's that charged the night before die, drift pins fall out of light stands, umbrellas come apart and woe is the soul that doesn't have a spare little cable.
Last February, a retaining clip on the cable attached to my tailgate release failed and I had one hour to figure out how to replicate my backdrop and reflectors which were now inaccessible in my truck bed. Six young ladies had gotten up early on Sunday morning to do their hair and makeup for headshots. I was not about to tell them and their Moms "a funny thing happened". I scrounged the dance school and found some black foam board and gaffer tape and a display easel. Bag was with me and I always have a little pop up 5 in 1 reflector. Doubled up the window curtains with gaffers tape for the hard winter sun. It looked like "MacGyver" but it worked.
Also, I'd planned to shoot some MF film. Checking gear the night before, my 645 FA 80-160 jammed and was unusable and had to be repaired. Used the FA 45-85 instead.
And so it goes.