It can be done. When we lost power during an ice storm a few years ago, I had to put all the fish from my 30 gallon tank in two one gallon tanks. Goldfish should be easier than tropicals because you won't have to worry about keeping them warm.

If you do this, keep the bucket in a cool spot to keep metabolism low, i.e. unheated garage, don't feed, and test the water several times a day to keep the ammonia level checked. You may have to do water changes. If you have an air pump and a stone, put it in there. And be sure to place something over the top to keep them from jumping out.

I routinely use a 5 gallon bucket to transfer or add new fish, I'll keep one in there a few days with just a bubbler. For extended times I borrow a filter from my tank and use it in another filter I keep just for that (both are tetra, a single and double tank filter). That way I jump start the bacteria. I use a 10 or 20 gallon rectangle tote box when I do that.

Makes an instant quarantine tank (and if you need one of these you need it in an instant).