Your equipment selection for Papua New Guinea is straight forward. Unlike the Mentawais or other popular Indo spots, PNG is consistently 3-4ft and fairly forgiving depending on where you are. Its very unlikely you will experience top to bottom 8-10ft kegs in PNG.
You should bring your everyday board, the one you love to ride at home. A backup board, one that will fill in if your go to sled is damaged in some way and as a matter of choice over necessity, a 3rd board that you either want to experiment on or a step up in case you do get one of the more decent swells that roll through when Micronesia gets a big swell or Japan is snowing its tits off.