(READ THIS INFO IF YOU EITHER HAVE TROUBLE FINDING THEM OR JUST SETTING A REMINDER)

Red Keycard (Dorms): Located in one of the apartment rooms, 2nd floor. This keycard unlocks the armored section of the militarized train station. This part of the station grants access to the enhanced versions of the military clothing (thicc)

Blue Keycard (Fisherman's Pond): Located in a trash can underneath a bag of garbage (the one with the yellow strap and black bag) This keycard grants you access to the weapons area.

Black Keycard (Heli crash NW of the Dorms): Located inside the cockpit of the helicopter. This keycard grants you access to the ammunitions area. Perfect place to stock up on ammo and high capacity ammo magazines.

Green keycard (every deadzone entrance (?)): This keycard grants access to the commonly open doors. Nothing special, but useful.

Purple Keycard (?) : I don't remember how I got this one, but it grants access to mining materials and such and a big gem.

There may be other keycards I missed. Please let me know in the comments below!