Can you take a fish on a three hour car journey without it dying?

He should get along swimingly.

put him in a largish plastic bag, with water from his bowl (a litre or so) and blow the rest full of air. twist and tie with a rubber band.

(get proficient at it, and you are qualified to work in a pet store...)

Fish love going for drives and hanging their heads out the window! He'll love it!

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).

wehen you bag up the fish use water from its bowl so the temperature is the same. when you release the fish float the bag in the new aquarium for an hour to aclimatise the fish to the new water temperature

When you put the fish in the bag do not fillet.

The chips are gonna be cold after 3 hours.

....but for heavens sake don't let the fish drive, no matter how much he begs.
To give the devil his due, they don't drive well, but are surprisingly good at parrallel parking.