Even with all the sealing and robustifying you've done, it's possible that things will break, usually at the worst possible moment. Here's what's in my repair kit. It fits nicely inside an Adafruit box, and makes me the Hero whenever someone's lights aren't working on-site.
I've got a butane powered soldering iron which works without being plugged in. This thing is great for onsite repairs, or repairs for a bigger project that can't be moved to a power source. I also have a bit of solder, solder wick, and a cleaner sponge.
Pack extra heat shrink and zip ties -- these don't take up much room but will save you for sure. For this design I'll pack way more zip ties since I need to cut them to change the batteries.
Extra batteries are a great thing to put in your repair kit as well. And be sure you have a screwdriver that will open your battery case. I love this fancy versatile one - it's like 8 screwdrivers in one.
The Gemma M0 is so inexpensive, why not bring an entire second Gemma-and-battery-pack assembly? That way if something goes wrong you can just swap out the whole thing and not need to worry about fiddly repairs. Same with the LED strips -- these are easy to change out and plug in. You can re-heat shrink using your butane powered soldering iron or a lighter as your heat source. And if you don't use them this year, you will be glad you have them on hand for the next project!
A thread ripper from the craft / sewing store is more useful than you can imagine. Everyone should have one of these in their repair kit. It's a small razor blade that can slice through seams, heat shrink, mylar, or a variety of other materials without any danger of cutting your fingers or going through wires -- so, perfect for repairs that need to happen after your second beer.
I always carry safety pins as well. A glue gun with extra sticks is really helpful too, though you'll need to find a place to plug it in as I've never seen a butane powered one.
Those little battery case screws are fiddly and small, and will get lost. Bring an extra battery case and some extra screws. Also throw in a roll of gaffer's tape (not shown) for when the zip ties won't cut it.
In case this isn't enough, here are a few links to commercially available products that are playa-tested and approved!
- Monkey Lights: POV light kit for bike spoke wheels
- Fun fur in lots of weights and colors
- Kick stand so you don't have to lay it in the dirt
- Bike baskets in various sizes and shapes