Burning is still used in many locations, followed by stirring the ashes. The can consist of anything from a bucket with a lighter to an industrial incinerator. Military units carry small safes in the field, and thermite grenades (basically a super-hot flare) that burn through the safe and destroy anything inside. Sensitive documents on ships (code books, etc) were traditionally stored in bags with lead weights attached, to be thrown overboard in case of boarding by the enemy.