Extras get far more use here than LEGO Star Wars, due to the new addition of the Red Brick, an extra collectible in every stage. Collecting it allows you to buy a new extra!
Unlocked: Start (250,000)
Not available in XBox 360 Version! If a LEGO Star Wars save file is located on the same memory card/device, than you can buy this Extra! This simply gives all the Characters from the first game that aren't also in the second. Neat, as you can get a Sith early if you need it. Some characters are downright useless because of alterations in Level Design (Jar Jar etc.), but others get the full LSWII treatment (Jango Fett).
Unlocked: Start (30,000)
When in Free Play Mode, some Levels will give you extra characters when this is turned on. Mainly for novelties sake, as most are useless.
Unlocked: Start (10,000)
A rather funny extra, turning this on and hopping on an animal will allow you to poop studs by hitting the attack button.
Unlocked: Start (10,000)
Causes Characters to wear a goofy mask with large glasses and a moustache.
Unlocked: Start (5,000)
Are you tired of boring old grapple hooks? Change them into daisies and flowers with this lovely extra!
Unlocked: Start (10,000)
Remember that scene from Empire where Chewie was carrying 3PO in pieces on his back? This simply adds that to Chewies model, so you can carry 3PO everywhere!
Unlocked: Start (5,000)
Wanna blow up the Death Star over and over again? This Extra changes the towable bombs into mini Death Stars!
Unlocked: IV-1 (Blasters; 30,000), IV-3 (Lightsabers; 26,000), VI-1 (Zapper; 15,000), VI-4 (Ewok Catapult; 50,000)
All these Extras do the same thing, make Weapons even better! Blasters and Lightsabers make them do double damage (With the exception of Boba Fett and 4-LOM, who now just slaughter everything). Zappers makes the characters that have Zappers actually able to destroy droids, and stun anything else. Ewok Catapult is awesome and hilarious, changing all Ewok's weapons into flinging torpedos.
Unlocked: IV-2 (Force; 25,000), V-2 (Build; 40,000)
Both of these Extras make these things, the Force and Building, go significantly faster than before.
Unlocked: IV-4 (40,000)
When playing a Vehicle stage, this gives your ship a Tractor Beam, making it pull in enemies. Can make things both easier and harder.
Unlocked: IV-5 (900,000)
Makes your character completely invulnerable to anything that isn't a pit. Extremely useful.
Unlocked: IV-6 (x2; 2,000,000), V-3 (x4; 6,000,000), V-6 (x6; 12,000,000), VI-3 (x8; 20,000,000), VI-6 (x10; 30,000,000)
Insanely useful, turning these one multiplies the amount of studs earned by the amount displayed underneath your character icon. The best part? They stack. Up to x3840. Have fun!
Unlocked: V-1 (20,000)
Any Droid character (who isn't IG-88 or 4-LOM), can now Self-Destruct to defeat enemies with the press of the attack button.
Unlocked: V-4 (290,000)
This Extra allows your health to refill over time if you've taken damage. Useful, but ultimately useless once you get Invincibility.
Unlocked: V-5 (500,000)
Really the first Extra you should aim for. This adds White Arrows on the screen pointing towards where Minikits are. This only shows where they are, not how to get them. Minikits that require multiple things to be destroyed, will show every individual thing.
Unlocked: VI-2 (75,000)
This Extra gives Boba (and by extension, Jango), use of Homing Rockets. Fired by pressing the switch button.
Unlocked: VI-5 (90,000)
This Extra gives every ship that's applicable, infinite torpedos in Vehicle Stages. Very useful.