When Jack says "Anyway, the conch doesn't count on this side of the island", he is clearly biting his banana and eating it, however the dialouge is heard perfectly clear, even though he is eating.
The attempt to make the locations look wild and uninhabited were obviously not altogether successful. Near the beginning of the movie, some boys are sitting in a sandy clearing in public-school blazers. On the right of the screen you can clearly see a tent peg with ANTONY M written on it. Also, as one of Jack's choirboy-hunters thrashes through the undergrowth, look closely and you can see that he accidentally impales an old beer can.