>>191758Also this, a knife, maybe a swiss army knife.
Could think about helmet if exploring caves, rope (but don't just get any rope, not all rope will support your weight, only try to use it if you know what you're doing), etc
Dust mask if exploring caves. Even with a dust mask be very careful. People die exploring caves from carbon monoxide (which is not detectable by your senses and is very dangerous, you pass out without warning and then die). Carbon monoxide meter could be useful. And dust mask could also protect against things like asbestos in abandoned buildings.
Also beware of hobos/squatters but chances are if you leave them alone they'll leave you alone.
