(I'll post a picture soon)
"Stim Pack" is the general name for all substances used to give you that extra bit of strength and stamina. They are mainly used by military forces, including the Galactic Defenders. They are used to give you the extra push you need if you get wounded and need to evacuate an area, or if your muscles are fatigued and you are about to be in a combat situation.
There are two versions of the stim pack used by GD forces: One is integrated into the armor, for when your biosensors sense that you need the extra strength. It is then pumped directly into your bloodstream, through a needle in your wrist. The other type of stim pack is a seperate syrynge, as you can see in the picture above, which is used by troops that aren't wearing armor. common methods of injecting it is through your upper arm, thigh, or neck. Some GD troops, even when they are wearing armor, will take off their helmet to use this version of the stim pack, as it is less painful.
Both versions of the stim pack use the same mixture of synthetic adrenaline, and other chemicals.