This time can be stretched somewhat by filling with oxygen, rather than air. Put the bags in a padded, compartmentalized container, and ship by air. For larger fish, or longer trips, one can use a sealed bucket for each fish, rather than a bag. Fish basically won't eat during the move. They're too stressed, and you don't want to degrade the water quality by the food, anyway.
Fish can survive a week or so without food if they've been previously well fed.
Try to maintain an even temperature, perhaps by placing the fish in a sealed cooler, or compartmentalized cooler. After the move, slowly condition the fish to the new tank location, as you would in adding new fish to a tank.