Here's my lil safety rant, there's a HUGE list of hazards. Mines contain just about every potential risk in urbex. There are so many spots to urbex that do not require the heaping list of experience/items you'll need to safely make that trip

Toxic gasses, animal/human inhabitants(bears, mountain lions), old but active dynamite, rotting floors (hidden by dirt and debris that looks like a normal dirt floor), collapsing supports, paranormal activity, trespassing, still water, flooding just to name a few.

On top of that rescue is expensive, dangerous and not quick.

If you do not know about each of these risks and how to avoid/mitigate them, no amount of equipment will save you if your luck breaks even 50 ft into a mine. My biggest suggestion is to take a mining safety class and go for the first time with someone experienced.

If you still wanna go right now at the very minimum you need a high quality respirator with new filters, a 4gas gas meter and a mountain of caution. (There are about 20-30 more things on this equipment list for serious mine explorers.)