You can drown the crabs in a finite amount of water. Keep their gills wet and they'll breath air. Dunk em occasionally or dump a bucket of new water over them in the cooler with the drain open.

Alternatively, you can clean and ice them until you can get them to your cooker.
_________________________
. . . and God said unto them, Be fruitful, and multiply, and have dominion over the fish of the sea . . .