Leeneia,

You should have more than enough material there to see you through your half hour.

For humorous songs, may I recommend Adam McNaughtan's "Cholesterol", and Jack Foley's "A Bottle of the Best". But quite honestly, the audiences at Highland Games in the USA (I assume the Games you are playing are in the USA) just love hearing the same old crap over and over again. Been there, done that.

Best of luck, and have fun.

Murray