A compact, minimal repair kit — small enough for your con bag — might contain:

• A handful of assorted safety pins. A good handler will always have these right on their person!
• Several feet of gaffers tape. Not duct tape. Don’t need the whole roll, just a few feet wrapped around a straw or pencil nub.
• Assorted zip ties.
• Straight and curved sewing needles, and 1–3 small spools of thread: black, white and neutral gray. Not a perfect match, but for quick repairs, these will blend at any reasonable distance, can replace later.
• Pocket multi-tool (e.g. Leatherman)
• One each black and silver permanent Sharpie markers.

Each costume might then have it’s own small auxiliary repair kit containing:

• Specific colors of thread and Sharpie pens for touch-ups.
• Specific spare parts, buttons, etc.

A more thorough repair kit for one’s base of operations (hotel room, car) might have:

• More of everything in the minimal kit (e.g. the rest of the tape roll).
• Hot glue gun and glue sticks.
• Cyanoacrylate “super” glue.
• 5-minute epoxy, toothpicks.
• A minimal electronics kit if your costume needs it; iron, solder, wire, tape.

Several people can share one repair kit. Be a good sport and take care of these items, keep them organized and clean, and replenish any contents after an event. Verify items like glues and markers are fresh and working.

Adafruit projects on this page: Phone-Activated Talking Dog Collar, DeLorean Time Circuit, Superhero Power Gauntlet, Wonder Woman Cosplay Bracers.