Enemies and some blocks drop small Diamonds when destroyed. These boost your Force power by a certain amount depending on whether you are playing the Novice or Pro mission. Other items can be found in capsules that are placed in predetermined locations throughout various stages. They become active as soon as you collect them.
Force Crystals
Item Capsules
This is the most common crystal. It provides 2 force units in the Novice mission, and only 1 in the Pro mission.
Collect this capsule to increase the number of extra lives provided for Luke by 1.
If you're lucky, a defeated enemy may drop this medium sized crystal. It's worth twice was small crystals are worth; 4 force units in Novice and 2 in Pro.
Collecting the pistol capsule gives Luke the ability to fire a blaster without the need to use the Lightsaber beam force ability. However, he loses the ability to swing the Lightsaber while the pistol is active.
You will only obtain this giant sized crystal by defeating one of the Darth Vader clone bosses. It's worth ten times the amount of a small crystal; 20 in Novice, 10 in Pro.
You will usually, but not always, find this capsule after you rescue a friend. Touching it provides you with a Landspeeder to ride. Push right to speed up, and left to slow down. The faster you move, the higher you jump. You are invulnerable to enemy attacks, and can mow enemies down, but as soon as you collide with a wall, the Landspeeder will crash and deposit Luke on the ground.
Companions
As you proceed through the game, you will gradually rescue six companions. These companions may help you at various points throughout the game if you communicate with them at key moments. Whether they help or not, you must rescue them in order to proceed to the next section of the game.
R2D2
Obi-Wan
R2D2 must be rescued from the scorpion Darth Vader on Tatooine. He will help you at a perilous moment in the Death Star.
Obi-Wan is a great Jedi master. You won't get very far until you rescue him from a jungle planet. He will guide you on the use of the force in important battles.
C3PO
Princess Leia
C3PO is held in an underwater prison. You'll have to swim to find him and battle a shark Darth Vader. Only he can help you make it past the stubborn guards on the ice planet.
Princess Leia awaits for you while captured in the Death Star. You'll have to make your way through the maze like fortress and locate her jail cell.
Chewbacca
Han Solo
Although Chewbacca is supposed to be the exceptional co-pilot of the Millennium Falcon, you won't rescue him from an ice plant until later in the game. His helpful role involves the use of his strength.
Han Solo is the glory seeking daredevil pilot of the Millennium Falcon… at least he was in the movie. He has virtually no role in the game other than as a rescue target, locked away in the rebel base of all places.