I'm actually glad he's doing this; Markipz would just have skipped everything important. Hell, I had to railroad him into picking up the Amulet when I did a text-adventure version of The Immortal, and that's supposed to be impossible to skip!
Besides, this is still Doom. How critically important could one piece of string be?
The armory is so named because there is a cache of body armor and medical supplies stored here. They look to be half-used, perhaps whatever's corrupted the men of Phobos Base doesn't care for med-kits and armor?
This Shotgun appears to be the standard-issue shotgun given to all Sergeants. It has three firing settings - Standard, Solid Slug, and Crowd Control. You've seen firsthand how powerful the Standard setting is at close range.
The shotgun is already reloaded; your wrists are not sprained, so there is nothing slowing you down when you fire or reload.
This standard-issue Armor appears to be the standard-issue armor that UAC gives to most of its people. It's green. Lightweight and durable, it can lessen the impact of bullets a little.
The Stimpack is a UAC first-aid kit, designed to be quickly used for health restoration. You could probably only recover a small amount of health from it, but there are tools inside to instantly mend broken legs and sprained wrists. Interesting that UAC includes those tools in both their Stimpack and Medkit.
Your Mod Toolkit contains the tools necessary to modify your weapons and armor... but only those tools necessary. It appears that you'd have to find actual Mod Packs on your own.
SKILLS:
Shoot Pistol (1 Bullet, 0 Rage, Normal Speed)
Aimed Shot P (1 Bullet, 0 Rage, Delayed Speed)
Shoot Shotgun (1 Shell, 0 Rage, Normal Speed)
Solid Slug (1 Shell, 0 Rage, Normal Speed)
Solid Shell (1 Shell, 3 Rage, Normal Speed)
Crowd Control (1 Shell, 0 Rage, Delayed Speed)
Boosted Healing (Automatic, Over Points are consumed to increase HP recovery when using healing items)