I've been gigging on and off for the past 35 years. During that time, as a drummer, I've had technical difficulties despite keeping my gear in good shape and taking care of it and doing preventative maintenance. Screws and bolts break. Things freeze up. Snare wires break. Drum heads break. Hardware fails. More likely, if you care for your gear like me, your guitarists doesn't have any tools to do a quick fix on a fatal tube amp problem.
As a drummer, I say it's dependant on you to be the anchor for the band. That includes carrying some pliers and screwdrivers so your guitarist can fix his amp. While you're at it, carry a box or two of popular sized fuses for tube amps so you can save the day. It is likely your guitarist, especially if a lead guitarist, will need at least one nine volt battery for his tuner as well.
I use a heavy duty medium sized padded shoulder camera bag or a backpack for my personal items, and it stays with me throughout the gig, even on breaks. It has wallet, cell phone, my DAT recorder when not recording, hearing protection and extra hearing protection, in ear monitors on the off lucky chance the venue has in ear monitoring, the DAT mic when the gig is done, extra t-shirt, hand towels, etc. If, hypothetically, you were a law officer permitted to carry a handgun off duty into a licensed establishment, this might also be an excellent place to carry your weapon or keep it while playing, as well as an extra mag and a flashlight.
I carry usually at least a spare snare drum head in my cymbal bag with the cymbals, encased in a pillow case.
Mrs. El Fisho got a nice gimme bag many years ago. It's a small, padded and heavy duty fabric satchel, just a shade too small for a laptop but perfect for a tool satchel. It has multiple dividers, and by using smaller containers to carry items, parts and tools, it fits into the SKB rolling stand case with the stands and is always there. She never used it and therefore I rescued it from a charity donation and it became my emergency drum repair bag.
I've used it for many, many years, and it's often com in handy. I keep it permanently stowed in the SKB stand case, except for the rare occasions I haul stands in some really nice red vinyl/pleather baseball bat bags. I have to break the stands down for the bags, but throw the emergency drum repair bag in as well.
Think of it as a gear fixing bail out bag for a drummer.
Although the case I use a thin and firm profile and edges, it is multi-pocketed and about 2" thick. Inside of that, I have several of the smaller zipper bank deposit bags made of canvas and vinyl that hold tools and or parts. I also have one of the pencil bags abandoned years ago by The Princess and rescued from charity by me.
Here's what I carry in my bag:
PARTS AND FIX IT STUFF
-either contained in a small plastic box from plano with compartments or in other of the other bags. Each bag and the box fit into their own segmented compartment inside the master bag, so everything is fairly accessible quickly.
*spare drum lugs of several sizes
*spare drum keys, including heavy duty DW key
*spare snare mounting thread and tape
*Loctite tiny small bottle
*Breakfree tiny small bottle
*machine oil teeny tiny small bottle
(note: all oils and fluids in a ziploc bag)
*screws/nuts/bolts matching those in drums for lugs and mounts
*extra small lug bolts and wing bolt for my DW pedal and tom mount(s)
*extra cymbal felts, the concave metal base that felts sit on and the top fasteners for the stands. I used the cymbal top fastener that is plastic and includes the plastic tubing that keeps the cymbal from rubbing on the stand mounting bolt. So I carry a few of each and a few tradition screws and tubing pieces.
*extra high hat clutch
*tuning/lug rods for snares, toms and bass
*extra set of snares
*extra wing nuts and bolts for cymbal stands, hh stand, snare stand, etc.
*extra dw memory lock
*basically any screw or bolt or nut that any piece of hardware uses that I have
been able to find for a spare.
*1 small vise grip pliers
*one leatherman tool with needle nosed pliers
*one tiny Snap On socket that fits the small nutdriver listed below
* one screwdriver handled nut driver with small socket and sockets for:
- various screw sizes for phillips and straight,
- and stardrives
that are used in my various drums. A very thin and small plastic box for all of the drive sockets fits into one of the bags along with the driver
*a couple of small interchangeable screwdrivers. one from a honda motorcycle tool kit, one from a toyota tool kit and some small ones from various sources.
*one small rachet drum key device that fits lug bolts for quick head changing
*one small hunk of duct tape wrapped around itself in a smaller sized package that a roll of duct tape in a plastic bag.
*a Tama Drum Dial, I've had it since 1993 and it works great. A real help in quick tuning in loud environments and it's small. Carry it in the plastic case it came in inside a padded mailing envelope to keep it safe.
*extra Radio Shack stereo condensor mic circa late 1980's in a small zippered case as a back up to the sony DAT Stereo mic normally used.
*an extra Danmar red maple beater (all I've used for 26 years)
I carry some unusual items that are quite useful. I have a selection of rubber tips that I can put on my spiked spurs to protect the floor, in various sizes. I have two doorstops if my bass drum wants to travel, and a couple of large old timey rubber stoppers to put my spikes into if needed. My gig rug has solved most of my problems, and I have reinforced rubber pieces to tape to the gig rug in case the gig is on a floor. Spikes will go through a gig rug, but the rubber keeps that from happening.
Since I bought a gig rug with a block of wood in the front, bass drum travel doesn't happen. But the various rubber tips and stoppers keep my spikes from penetrating the gig rug onto the floor. HINT: my spur spikes are long and sharp. I put washers in the bottom of the rubber tips, so the tips wouldn't be damaged but so the tips won't penetrate the bottom of the rubber tip. I usually keep a set of rubber tips on the spurs themselves but like having backup pairs.
With the exception of the microphone and the Drum Dial, the tools I carry are in a zippered small bank deposit bag, Some are in their own roll up cases, and some are in a smaller zippered bag. It makes finding stuff easier in an emergency.
I have a small first aid it and some aspirin and other stuff that goes in the bag as well.
Extra Falam! pads both large and small for the bass drum in the rare case I might start damaging the drum head (which already has a small Falam! on it). If it did begin to tear, a larger Falam! applied over the smaller would likely get me through the gig. Since I began using Falam! pads on the bass drum, I have not had any broken bass drum heads.
I also carry a couple of the Ludwig adhesive Power Dots that went on their popular 70's tom and snare heads. Essentially a layer of drumhead with adhesive underneath, if a tom or snare head begins to give away or does tear, one of these can get you through a set or gig.
-Stuff I carry for guitarists to keep the gig from cratering:
*two sets of electric guitar strings
*two nine volt batteries
*two tiny boxes of amp fuses
*a guitar cable (George R, thin and good).
This stuff has come in handy many times. Once, I could see a snare head begin to crack, and layed off of it for the rest of that song. A quick Power Dot applied, and a little retuning and it was fine for the rest of the gig. I've had bolts on the DW pedal come loose, hence the loctite and spare pedal screws and bolts.
So in a smallish 10" x 8" by 4" malleable bag I have most of what I need in an emergency, and most of what I need to rescue a guitarist so the show can go on! The bag is really about 3" thick, except for the bulge of the Tama Drum Dial which is a bit thicker.
The bag rides nicely in the SKB stand rolling case, and stays there. Because it's padded, it stays put and doesn't get slammed against the other contents of the sand case. It doesn't leave the SKB case unless needed at a gig.