I thought a thread like this could be useful and/or educational.
Aside from all the shit that makes your gear work and your merch, what do you bring to your gigs?

As a drummer I bring extra felts and wing nuts, some moon-gels (though I rarely use them), If I am supplying the kit for the gig I bring an extra bass head. I always make sure i bring a knife and a flashlight. It's also good to have rolling papers on hand so I keep some in my stick case.

blank paper
sharpies
gaff tape
small bills to make change for purchases of merch
business cards
small assortment of hand tools
earplugs
aspirin

First off, this is a really good/useful idea for a thread!

I feel that I'm one of the more prepared/paranoid members of Reaver so I'm pretty decent at being prepared for shows. Here is my list of things I bring/do before any given show:

String winder
String cutters
Extra pack of strings (both sit on my amp during the performance too)
Screwdriver to make sure straplocks aren't going to pop off
Extra strap
Pack of extra nine volt batteries for wireless/anyone who needs em
Lots of different size picks
Change for merch/ cash box
Extra butterfly clips for merch booth
Sharpie
Many set list copies
Masking Tape
Extra guitar cable
Extra guitar just in case
Guitar rack
Extra AC Adapter

I feel like there is more but I can't think of it at the moment. I turn into a paranoid stressball about 3 hours before any show

I travel with a repair kit that contains:

4 packs of strings
String winder
Pliers/cutters
Screwdriver
Little tripod neck stand thingy
Different sized wood blocks to block my floyds
Soldering iron
Solder
Multimeter
Spare jacks
Wire
Masking tape
Electrical Tape
Aerosol contact cleaner
Flashlight
Sharpies (black and silver)
9v batteries
Spare 9v adaptor
Spare Tubes (I just saved the old ones, they were still working fine. It's not like I'm wandering around with $200 worth of unused glass just for the fuck of it.)

And something unfixable still happens every so often. I always thought a backup head and cab were overkill, but I've had to use another man's amp at a show once when my shit fried out.

One extra skin for each drum
Towel
Dry shirt for after the gig
Deodorant
Extra set of in-ear headphones
Extra 1/4" cable for forgetful guitar/bass player
Power bar in case there's a shortage of power outlets
Spare PSA adapter for metronome
At least 2 of each cable required for the gig
Spare bass drum pedal
Spare beaters
Gaff tape
No less than 3 pairs of sticks

I bring my arms so I can cross them and stand at the back of the room and not move. I keep an extra pair in a vault.