Safecracking
Kirk Douglas opens both the nitro safe and the wagon safe in seconds, but he's Kirk Douglas and the audience doesn't want to sit around for the time that it would actually take to do it.
The problem is that the safe in the war wagon is laying on its side, and on safe combination locks the fence falls into the wheel notches under its own weight, so that even if Kirk knew the combination the lock wouldn't open unless the safe was upright.