I just did it coming back from florida in June. Had them in a bag just like getting it from the pet store. Took them out of my carry on when I got up to the invasion of privacy equipment and handed it to the TSA person. He looked at me weird and took them to probably his superior to find out what to do. Lol. As long as the fish are alive in the water it should be fine. Just dont send them through the xray machine.
You can put them in your checked luggage. Less hassle. Get some wide mouth bottles like Gatorade comes in and put a fish or two in each bottle. V8 juice comes in a larger bottle I think. THere is not much chance that the bottle will break even if the bag is thrown around. However if you DUCT TAPE the lid on, it is also unlikely to leak. Treat the bottle just like a fish bag and fill it less than half full and use one of those declor liquids (at the level recommended on the bottle) that consume ammonia and the fish will be good for more than a couple days.
You might even find a very wide mouth pickle jar that is make of plastic for bigger fish. I would not recommend using glass jars.
I've also heard that it's good to call ahead to the airport as well as have the TSA page printed out and with you. The amount of awareness of the policy varies from airport to airport. If you're flying through an area that's rich with hobbyists that do this on occasion they are probably more familiar with it than in other areas. I did recently read a Facebook thread from a friend who had to get rid of the fish because they wouldn't allow them on even though the policy says its ok.
Carry on is riskier than checked baggage.
I also know of someone who has a styrofoam cooler that exactly fits in one of his pieces of luggage and frequently uses it for travel.