Make sure you don't get them too cold. Anthing below 45 degrees can kill them. Crabs should be kept anywhere from 48-55 degrees.
I would put a layer of ice in the bottom of the cooler and then the crabs on top. Then put a small oyster sack (or something to keep them moist) and close the lid or keep it just a little open and put a little ice on top of them.
I've also heard to keep them tight so they don't fight with each other and kill each other. Another thing you want to do is pick out the dead ones because most likely they will be mushy and won't taste as good.
This post was edited on 7/11 at 6:18 pm