The skipper is carrying a big load of bananas to take back to the huts. They are almost completely green. When the skipper arrives at the huts, many - including one full bunch - are yellow (ripe).
With all seven of the castaways watching for something, it seems impossible that Gilligan was the only one to hear a helicopter approaching, much less landing and taking off.
The Howells are famous. Is seems odd that Barkley doesn't know who they are.