Easy Experience and Loot
Head to City Wok, where you will find two elf kids near the front of the store. You can attack them and easily defeat them for some quick experience. Then enter City Walk and save your progress before exiting to find that the elf kids have returned. You can repeat the process as often as you like, easily obtaining experience and loot. Make sure that you pick up any goodies they drop, though, since the kids may not materialize if you've left a bunch of stuff lying around.
Cherished Emmy Awards
The South Park television show has thus far won three Emmy awards, for episodes aired during the 2007, 2008, and 2009 seasons. Check the sewer vents while playing the game and you will find Emmy awards, implying that they were flushed down the toilet.
Tom Cruise Reference
Visit Stan's house and enter his room, located upstairs. Once there, note the closet to the left. An unseen someone will shut the door to the closet and announce that "I'm never coming out," an apparent reference to the episode in Season 9 of the TV show, "Trapped in the Closet," where Tom Cruise refused to exit the closet.