Which career does Tom want to take up?

Tom Sawyer considers several careers in chapter 8. After Becky rejects him, he wants to run off and start a life of adventure., that way he can return to St. Petersburg someday long in the future and make everyone jealous of his accomplishments. He thinks about several careers that could support the lifestyle of a roguish adventurer who explores the world. He briefly considers being a clown, a soldier, and an Indian. He eventually decides that a career as a pirate would suit him best:

He would be a pirate! That was it! Now his future lay plain before him, and glowing with unimaginable splendor. How his name would fill the world, and make people shudder! How gloriously he would go plowing the dancing seas, in his long, low, black-hulled racer, the Spirit of the Storm, with his grisly flag flying at the fore!

Tom fantasizes about the glamorous life of a pirate captain. After a long career of swashbuckling on the Seven Seas, he would return home to his little town a legend. He clearly likes this idea as we can see later, when he and his friends Huck and Joe play pirate out on Jackson's Island.