A stamp.

Wheelbarrow.

A promise.

None, because it would stop being empty.

The answer is either daughter or son-in-law, depending on whether the speaker is female or male.

E, the first letter.

8, 5 in church more 3 for every thief

He is a pilot in the cabin of the airplane.

Mississippi.

Neither. The ambulance doesn't put out fires.

18 eggs.

1 chicken lays 2 eggs in 3 days, so 3 chickens lay 3×2=6 eggs in 3 days. In 9 days, these 3 chickens lay 3 times as much eggs as in 3 days. Conclusion: three chickens lay 3×6=18 eggs in nine days.

The plane was still on the ground.