Forget the small bag a goldfish came home in: an emergency kit for a goldfish starts with volume, because this is a large-bodied, heavy-waste fish that can foul a small container and burn through its oxygen in hours. Everything else in the grab bag — air, testing, spare water treatment — exists to buy a goldfish time in that temporary container until a proper tank or pond is running again.
A container sized for a goldfish, not a minnow
The centrepiece is a sturdy, food-grade plastic tub with a secure lid, big enough that the goldfish can turn comfortably and the water has some depth. Bags are a poor choice for anything but the shortest hop: a strong fancy goldfish can split a seam, and a bag holds too little water for the waste this fish produces. Pack the tub clean and dry, never washed with detergents, with a soft net wide enough to lift the fish without folding its fins. If you keep more than one goldfish, plan a tub per fish or one genuinely large shared tub — crowding evacuees together concentrates ammonia exactly when no filter is running.
Air and ammonia: the two clocks running
A battery-powered air pump with an airstone and spare batteries is the most valuable item after the tub, because a goldfish in warm, still, waste-laden water is short of oxygen long before it looks hungry. Water conditioner that also binds ammonia belongs beside it, along with a simple liquid test kit so you are checking the water rather than guessing from the fish's behaviour. A sealed jug that you fill with conditioned tap water at departure time gives you a first water change ready to pour, sparing a stressed goldfish the wait while a host measures conditioner at the sink in an unfamiliar kitchen. A thermometer completes the set: goldfish tolerate cool water well, but a tub left in a hot vehicle climbs in temperature while its oxygen falls, the worst combination for this fish.
Food: pack a little, plan to skip most of it
Include a small container of the goldfish's usual pellets, pre-soaked feeding being impossible to arrange mid-evacuation, but treat food as the lowest priority in the kit. In an unfiltered tub, every meal becomes ammonia, and a goldfish in decent condition handles a short fast far better than a day of rich feeding in dirty water. If the stay stretches, feed a fraction of the normal amount and change part of the water afterwards. One exception: note on the kit card if the fish is a delicate fancy variety, such as a ranchu or oranda, because those fish tire and struggle in currents or deep water that a comet would shrug off.
The card a goldfish host actually needs
Record the goldfish's variety, approximate length, normal portion size, and any ongoing issues such as swim-bladder sensitivity or a healing fin, in words a non-specialist can follow. State plainly that the fish needs dechlorinated water and regular partial changes in any temporary home. Keeping the full version of that record in KinsLe Pet Passport means the tub, the test kit, and the goldfish's own history arrive together wherever the fish is sheltered.