Crappies are not known as picky eaters. The popular pan fish will go for worms, insects -- and egg shells. Crappies don't really want the egg shells, but they can think the white flakes are minnows. When they attack those flakes and find no minnows, chances are they will settle for the real bait on your hook.
Place the egg shells in a plastic bag and crush them with your hands. Crush at least 10 egg shells for a long fishing trip.
Sprinkle the equivalent of two egg shells in the water where you suspect crappie are schooling. Cast a jig as normal with regular bait.
Add more egg shells around the casting site every 30 minutes or an hour depending on how the crappie are biting. If there is a strong current, you may need to add more since the water will carry the flakes away from your site.