I have had good luck keeping them on a stringer
I have come back to the dock late at night and left them in the water on the stringer and in the morning they are swimming around and doing fine, ready for the knife
most times I hit them over the head to kill them quick, I have stuck them with a knife through the eye into the brain
and it's best to cut their gills to drain the blood if they are going to be there a while
walleye are easy to just snap their backs behind their head, but I have never tried it on other fish