"How 'd Ya Like to Spend Christmas On Christmas Island" isn't an original Buffett song, although it fits right in with his own songs. It's from the 1940s.

I sing a few Buffett songs fairly often, either solo or in song circle/sing-alongs:

The Captain And The Kid
Pencil-Thin Mustache
Come Monday
and, of course,
Margaritaville

I used to do "Growing Older But Not Up," but it's been so long since I've sung it that I've forgotten most of it.