Could you explain this humor? I pretty don't get it.
Native speaker’s answer
Rebecca
"How long did you think this barbecue was gonna last" is said here as a joke because Ross came into the room with a bunch of luggage. Since they didn't know until he told them that he is going to China, Phoebe made a joke about him bringing all the luggage for the barbecue as though he packed for it thinking it would last for a long time.