You will need the rocket launcher (gained from killing rocket-creeps and picking up their ammo drops) to access two of the collectable areas.

Some walls have fracture lines. These are destructable. The gun is the first collectable to retreive followed by the armour?. The helmet is accessible without destroying any walls.

There are several first aid kits and ammo packs when accessing the armour? piece of the collection.

Simply pass through the destroyed wall area and proceed as far as possible to get the gun and armour? respectively. The helm is readily accessible (hence only the single screen shot)