ooooo, oooo! I think I can actually take this one! *stands up straight with a suave boyish grin* you know...being a fellow adventurer's club member myself. "Koongaloosh!"
Haha, in relation to the songs that they sing in the library though, they are more or less %100 original or atleast have one of the most original takes by the members of the club, depending on what night and show they decide to do that night.
If you make it into the "Hoopla" (the main event of the night in the Library), then you will always here the opening sing-along of "the happy wanderer," usually sung by our club's very single singer and biter herself, Samantha Sterling, and usually ending in the club's rendition of "oh when the saints go marching in," where they take turns creating their own verses.
Usually, there are two or three songs inbetween that they like to mix up every night, depending on the show they choose for the hoopla, and if it's a special holiday. Personally, some of the holiday ones get to be hilarious.
Here are some of the ones i remember as i skimmed through youtube (am i allowed to link from there? hope i am, if not i'll take them down)
http://youtube.com/watch?v=eFExAJ5U0eQ <----Under the Scottsman's Kilt
http://youtube.com/watch?v=sD74F1iispU <---- Florida, the moon, and I
http://youtube.com/watch?v=tf8LgOq_Tg0 <---- Oh When the Saints (Adventur's style)
My favourites:
http://youtube.com/watch?v=zGhPbl6mxYY <---- Icky Yucky Sushi ( I haven't seen it in person, but MAN i love the song)
http://youtube.com/watch?v=ZIZ7rXFleAs <---- I'm Your Mailman (the dirtiest Disney World should ever be able to get...but JEEZE IS IT HILARIOUS)
http://youtube.com/watch?v=SL_tbJxopus <---- Lonely Jew on Christmas (an example of the Holiday show)
I hope that is what you were looking for? Keep searching if you want more, cause trust me, there are. If i find any i'll list more...or if i ever find an "official list"