Crab:
Best to marinate your chicken, salmon (or other preferred meat or fish heads) overnight in a zip-lock bag. Stuff the marinated meat into your bait container. I usually slather an additional 1/2 cup over the whole thing and then drop it over the side and let it soak. They can't resist the smell and will travel great distances to get a bite.
Shrimp:
Four cans Friskies Ocean Fish, 5 handfuls of Hikari Koi food, 32oz of Bob's mixed the night before. Added more Bob's when I dropped the pots.