I was actually looking on a Scouting site that has explained a possible meaning of gin Gan Gooly which is relating to a Grey Ghost elephant that comes wandering after the rains, when the elephant reaches a village it would either walk through it or go round it. If it walked round the village would be prosperous and if it went through they would be hungry and suffer bad crops. In the tribal village of Watcha the leader Ginga Gool (or something like that) was troubled by 3 years of the elephent going through his village. He arranged spearsmen to chantand frighten the elephant to go round and his Medicine man (Hayla SHayla) to make magic potions and throw them around village (Shally wally shallywally) and the elephent replied Oompa Oompa Oopma this went on and the chants got louder and eventually the elephant swerved round the village - thus the oompa getting quieter.
Or it could just be the most common explanation in that it was easy for scouts and guides round the world to pick up!!
Braw to remember camp fires though.
Rolling home blind drunk was my fav!!
By the light of the silvery moooon
laughing ha ha hee with a bottle on my knee
and the shadow of my top hat on the wall!