Use a wire minnow trap (
Do not buy or use a plastic coated trap, they are junk and do not trap squat)
bait the trap with chicken,
fish heads ( keep the heads from touching the sides, forces the crayfish to find a way inside or they will sit on the outside of trap and eat the food),
Tunafish can (stab holes in it),
cheap dogfood ( I know Dads works well, some other brands dont work at all),
catfood cans (stab small holes in the top so the smell leaks out)
Cabela's sells a square wire trap I have had minimal luck with it.
Frabill makes a black thread type saltwater Crab trap that works real well for the bigger crayfish. I have yet to find an online dealer who has them. I bought one while visiting Florida one year and havent been back since.
Make sure you leave the trap out overnight Crayfish love feeding at night.
or if you have kids send them down to the creek to flip over rocks and catch crayfish.