First, there are 55 Dark Horse comic book pages to unlock, after every mission three pages appear, the rest come after you beat the game. Second, there are 23 trading cards to collect. One trading card will appear for every Mandalorian Feather that you locate. Note: There is one feather in each level. The other cards appear after you beat the game.
Third, for every 2,500 credits you collect on a secondary bounty, one page of concept art will appear. This means to collect all 110 pages, you will need 275,000 credits.
Now on to the strange Easter eggs.
Find a Power Droid (the ones called "gonks") and bump into it FIVE times. Afterwards, the droid will exclaim strange beeps that sound like Morse code. It is Morse code actually. The Morse code is a declaration of allegiance to a game designer.
Next egg, find the Beast Handler and follow him back to his home without shooting him. In his home is a sculpture of Devil's Tower out of some kind of mashed potatoe thing.
Last but not least, find a green sign on top of a building (I'm not exactly sure which one). It has the phrase on it that says, "I'm selling these fine leather jackets," which has appeared in about every other LucasArts game.
Tap these phrases in the Codes Screen:
SEEHOWTHEYRUN:Chapter 1
CITYPLANET: Chapter 2
LOCKDOWN: Chapter 3
DUGSOPLETY: Chapter 4
BANTHAPOODOO: Chapter 5
MANDALORIANWAY:Chapter 6
GO_FISH: All Cards
R_ARTISTS_ROCK: All Art