Hard hat good pair of boots/shoes, flashlight,gloves if your hands get cold. But they may have most of the things needed at the time of the tour.
Also, if you go in any of the ones you need to crawl in, a pair of knee pads would be helpful.
You may want a good coat, too, and make sure it is a good, strong flashlight (mine was too weak). Otherwise, what Doug R. said.
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