It depends on the fish. If it's a small fish you may bag it or put it in a small container. If it's large fish you may ask the person coming to get the fish to bring a bucket or large container.
I am selling a pair of clowns about 1-1.5". I don't have any of those bags that the fish stores sell their fish in. I'll try to get some. Thanks for the advice
Never thought about a ziploc bag.
I'm always nervous about air. Some LFS blow air into the bag. Guessing for a small commute, air supply in the water should be sufficient.
It won't matter for a quick commute. I usually use the 1 gallon bags. You can trap air in the bag yourself. Blowing into the bag isn't a great idea. When we exhale we release CO2.