Keycards
Keycards are one of the main items in the game, being used to unlock locked doors to progress on through the facility. There are three types of cards that can be obtained: the blue keycard, the main one you'll come across, the purple keycard, another one that's guaranteed during a playthrough, and then the code breacher, a red keycard that you can be lucky to find or buy at the beginning of a playthrough before the game starts that is able to unlock any door.
Lighting
There are a few different types of lighting that you can come across during your playthrough, some that you can even buy from the pre-round shop. Lighting isn't required to get through your playthrough, but it does tend to make it a bit easier. The flashlight is your typical light source, however it has a durability and once it runs out, you will need to replace it with a battery. The lantern is similar, but has a shorter durability and also requires a battery to charge it again for more use. The hand cranked flashlight is the only flashlight-like light source that doesn't need a battery to recharge. It can be noisy, however, making it harder to hear for enemies. The flash beacon is the only light source that does not stay on while you're holding it. Like in the name, it emits a flash of light that will light up the room for a brief moment before needing a second to recharge. The blacklight is similar to the flashlight, but just like its name, emits a blacklight effect, having your surrounding have a purple tone. Just like the other light sources, it also has a durability that needs a battery to recharge it.
Healing/Health
During a playthrough, you'll have a health meter in the corner of your screen. Your health won't naturally regenerate, so you need to be careful during your playthrough. There also aren't a lot of options when it comes to healing. There is a medkit that you can buy in the pre-round shop, or you can find one in one of the rooms you go through. Another item you can get, while rare, is called a wall dweller chunk. You can either buy it from Sebastian's shop if its in stock, or you can get it from a wall dweller corpse if a node monster came through the room while it was active. It is the only item you can consume that can slowly regenerate your health.