"I Am Not Your Gameboy" song - Successfully complete all songs in Guitar Duel mode to unlock the "I Am Not Your Gameboy" song.

Bonus guitars - Successfully complete the indicated task to unlock the corresponding guitar at the shop in Career mode:

ES-335: Get a "5 Star" rank on all songs on a CD in Medium mode.
Les Paul Dbl. Cutaway: Successfully complete all songs in Hard mode.
Moderne: Get a "5 Star" rank on all songs on a CD in Easy mode.
Synapse: Get a "5 Star" rank on all songs on a CD in Expert mode.
Vanguard: Get a "5 Star" rank on a song in Expert mode.

Bonus guitar finishes - Successfully complete the indicated task to unlock the corresponding finish at the shop in Career mode:

Blue Synapse: Get a "5 Star" rank on all songs in Expert mode.
Custom Cherry ES-335: Get a "5 Star" rank on all songs in Medium mode.
Custom Rising Sun X-Plorer: Get a "5 Star" rank on a song in Easy mode.
Ebony Firebird: Get a "5 Star" rank on a song in Medium mode.
Orange Vanguard: Successfully complete all songs in Expert mode.
Pale Yellow Moderne: Get a "5 Star" rank on all songs in Easy mode.
Rootbeer Les Paul Double Cutaway: Get a "5 Star" rank on all songs in Hard mode.

Bonus costumes - Successfully complete the indicated task to unlock the corresponding outfit at the shop in Career mode:

Axel's No Shirt: Successfully complete all songs on a CD in Expert mode.
Axel's Other Shirt: Successfully complete all songs in Medium mode.
Gunner Jaxon's Random Junk: Successfully complete a song in Easy mode.
Gunner Jaxon's Whatever: Successfully complete a song in Hard mode.
Johnny's Anarchy: Get a "5 Star" rank on all songs on a CD in Hard mode.
Johnny's Ink: Successfully complete all songs in Easy mode.
Judy's Flashback: Successfully complete all songs on a CD in Medium mode.
Judy's Pirette: Successfully complete a song in Expert mode.
Memphis Rose's Biker Gal: Successfully complete all songs on a CD in Hard mode.
Memphis Rose's Recruit: Successfully complete a song in Medium mode.
Pandora's Bad Apple: Successfully complete all songs on a CD in Easy mode.
Pandora's Lace: Get a "5 Star" rank on a song in Hard mode.

Faster credits - At the main menu, select the "Credits" option, and strum the touch screen to make the credits scroll faster.

Easy auto-whammy - When you have long notes, instead of whammying many times, strum, whammy, and drag the pick to the top of the screen. Then, keep the pick there and the game will whammy by itself.

Easy Star Power activation - Instead of shouting "Rock" into the microphone, just blow into it to activate Star Power.

Chord with no fingers - If an opponent uses the bomb weapon and you play a chord (two or more notes at the same time) that is long and is a bomb note, it will play itself without your fingers on the frets. You can also push any desired fret while the note is sustained, but if you strum the guitar, the note will stop and your opponent will get some of his or her meter back.

Flipped screen in Guitar Duel - Whenever your screens get flipped in Guitar Duel mode, you can still strum the touch screen and get points, even though both screens are flipped.

Lars Umlaut reference - When you get hit by the Signature battle item in a Guitar Duel and the fan asks for you to sign his or her book, Lars Umlaut's name is on the top of the book.