'g-dog' would be been a good one too.
The food I've liked in my time is American country cookin'-Colonel Sanders

Bud calling Gordon "GG" was to show the progression of their business relationship. Early on in their first meeting Gordon refers to Bud not even by his name, just "pal" while Bud is calling him "Mr. Geckko." Later on, Bud starts calling him "Gordon" If I recall correctly the "GG" term didn't come until later in the film when they're aboard Geckko's private jet. I suppose only members of Gekko's inner circle are allowed to call him that, which Bud had obviously become a part of.