I use a small aluminum bat. One good whack and they are stunned / dead.
The thunk / ping sound is cool.
I then put them in the cooler and put ice over them. Each fish gets layered in ice.
I use to put them in alive and put ice on them. Often - they would flop around and end up on top of the ice - not buried under it.
Other way - just use stinger hooks - it kills them everytime
