Yep, cooler should be good. I'm considering flying down that Sunday morning and doing a day trip, returning that night. I have a ton of Skymiles and less money spent on travel = more money for corals. How common is it though for vendors to hold until Sunday if bought that Saturday? I've never been to anything other than a local show where transport is not a problem. If I drove, I would have more options. I agree, not really necessary, but which is more stressful keeping a coral in a bag for about 24 hours or trying to maintain water circulation and constant temperature with water the corals weren't grown in?
Regarding air travel:
Live corals in water and a clear transparent container are allowed after inspection by the TSA officer.
www.tsa.gov