What kind of precautionary measures would you take, if you planned on exploring something abandoned?

Something big and slightly far away from civilization. Like an abandoned hospital, factory, school, something like that. Or perhaps go to a higher level; abandoned mines, sewers, or an entire abandoned town. Let’s leave out small things like houses or graveyards.

Can you make a list of precautions you would take if you planned to explore something abandoned? Please keep in mind, I’m not looking for morality based answers, such as breaking the law by trespassing, or opinions on how one would never dare to explore something abandoned. I mean if the place is protected by the authorities, obviously, you don’t go. (and in that scenario, anyway, it’s not really ’‘abandoned’’)

This is my list, can you add to it, or comment on it? What would you do?

My first rule is, don’t go alone. A group preferably, so if something happened to someone, it would be easier to help them, or get help, if needed. Bring a phone, as well. (not just for taking cool pics, but also for help)
Bring water to drink. Bring snacks. (sealed, preferably)
Toilet paper, in case you gotta go. It happens, man.
Bring a flashlight, and a first aid kit. (band aids, pads, shit like that)
Wear gloves, especially if climbing is involved; but avoid climbing if possible.
Bring a whistle, not just for help, but to scare wildlife, if it’s brave enough to approach you. If the area you plan to visit is an obvious home to wildlife, then do not explore.
Pick a nice day, no snow or rain, and don’t go at night.
Just a little personal one for me, respect the place. Don’t start breaking everything just for the hell of it or anything lame like that.

I was going to add, bring a weapon of some kind, like a crow bar. Thing is, it’s probably not necessary. If anything though, the crow bar could be used on locked doors and such. (this kind of goes against my last rule, but at least it’s not completely pointless destruction) I’ve been in old factories and stuff as a teen, but we never needed anything to open any doors, and most of these places, the doors weren’t even there anymore, besides the main ones. (of course, there are tons of abandoned places everywhere, which all vary greatly)

What is your list? Whether you have experience in exploring abandoned sites or not, let me know what you got. What important steps would you take before undergoing the exploration?