It was basic campfire sing-a-long stuff. A bunch of Beatles, Simon & Garfunkel, John Denver... stuff that old farts like myself who grew up in the 70's would know. Progressions were were simple (lots of A, D, G, and other guitar-friendly chords) so whipping up a countermelody, taking a solo (since no one else wanted to) and/or adding a well-known hook line wasn't a biggie. Pretty amateur stuff, but it was fun.