@The Pentacle Queen,
In addition to what rockhead said, if you go to a pet store that sells fish they can fill the bag with pure oxygen, which allows for even more transport time without worry. But three hours should be fine as long as you have enough air and water in the bag (I've found ziplock freezer bags to work well for this).
Do note that transporting the fish can shock it, and that there are timed-released feeding options available as well. I've used an electronic timer that released food daily, as well as pellets and discs that had timed release of the food (there's a gel-based disc for this that I like best).