Explain the meaning of Huck’s expression: “There warn’t much sand in my craw”. (38)

The expression "sand in your craw" has come to mean someone who is feisty or plucky, like the bird fighting for its life against the farmer. If you don't have much sand, you are not courageous or feisty. Often, the phrase was shortened to just "to have sand." Oh, and "warn't" is just dialect for "wasn't."