Access Lost Levels
Get a minimum score of 300,000 points, then at the Title screen, select Luigi.

Access You vs. Boo
Get a minimum of 100,000 points, than at the Title screen, select Boo.

Album Pictures
Perform the following actions in any order:

Clear world 8-4 (2 pics)
Get fireworks after a level
Find a hidden 1-up
Find a bean stalk
Kill a Goomba
Kill a squid thing
Kill Latiku (guy who throws Spinys)
Kill a fish
Kill a Hammer Bro
Kill a bullet guy
Kill a Koopa Troopa (any)
Kill a beatle guy
Kill 4 Bowsers

Level Select
Beat the first quest.

Play Japanese Super Mario Bros. 2
Beat Classic game twice without warping.

Play as Luigi
At the Map, press Select. Press Select again to revert back to Mario.

Unlimited Continues
At the Game Over screen, hold A to continue