The best:
2. Sell Gravel and get rich
3. Teleport extremely fast repeatedly and fly.
Some things that would also be good:
5. Would be funny to prank people by making every toaster in the world go off at once
9. You can tell if a container is empty.
8. Name the language something else and mess with people using it.
Things that would be good conditionally or in niche situations:
9. If you're an extremely slow runner
6. give to a dead person
1. Have an oyster pet