What did Elisha do with his oxen before following Elijah?

Answer: Slaughtered and cooked them

Elisha slaughtered his pair of oxen, cooked the meat using the oxen's equipment as fuel, and gave it to the people.

“So Elisha turned back from him, took his pair of oxen, and slaughtered them. Using the oxen’s equipment for fuel, he cooked the meat and gave it to the people, and they ate. Then he set out to follow and serve Elijah.”— 1 Kings 19:21 (BSB)