After too many similar situations, i finally got smart and put together an emergency bag that lives under the seat of my truck, containing a spare mic, mic cord, spare power supplies for every piece of equipment i use, sax strap, and a couple standard power cords (a 50 ft extension cord lives under the other seat). And i leave a keyboard stand, mic stand, and folding bench behind the seat. Though i did have to have my wife bring my expression pedal to a (band) gig one time, so may need to add spares of that and a damper pedal too.
I do have a list to make sure everything that should be in my big bag of cables (audio, speaker, MIDI, power, etc.), pedals, mixer, etc., gets packed. My big fear would be arriving at a gig and realizing that the bag i so painstakingly packed was sitting at home on the practice room floor.
- Jimbo