-Active Camoflauge

Rarer than the Overshield, Active Camo renders you nearly invisible. Cloaked players are almost impossible to see from a distance. Firing disrupts the cloaking field. Elites and some Flood Warriors use these in campaign. In multiplayer, snipers and sneaky players love to hide themselves under cloaking for sneak attacks. Note that in multiplayer, cloaked enemies still appear on your motion tracker, and an enemy will partially decloak when hit by enemy fire.

-Overshield

Notes: The Overshield increases your shield to 300% power, prolonging your life in a firefight. However, Oversheilded players are still vulnerable to the Shotgun and RL. Overshields do not recharge until they are below normal level, and in multiplayer they slowly drain away. Note that the Plasma Pistol's overcharged bolts will still completely bring down the shield. Fun things to have; nothing beats the look on your opponent's face when they empty a whole clip of AR rounds into you and you don't get hurt. :D

-Medkit

Notes: The Medkit is your loving friend. :) It will take your armor back up to 100% when collected. In campaign, it is a good idea to conserve Medkits whenever possible; in multiplayer, go ahead an deny your enemy the use. :)