Good info by 4x4. Get all the metal out first, and I know by experience that you will have roots to cut, SO, take your time, it will go nowhere. If you find nothing else you will have experience that you can tell the children and watch their eyes widen while you talk. Enjoy the trip.
With so many nails in it, someone was determined to keep the lid ( or bottom ) on. This could have been used back when folks salted the pork meat down in boxes.