This is a nice little challenge. I have done each of the suggested things, leave, chat and make friends. Naturally, it somewhat depends on who you sit next to, some people are engaging and others definitely want to be left to themselves.
I have found it a great opportunity to learn about others and to explore the art of conversation in an unfamiliar setting. Some truly lovely people have sat next to me and I feel grateful for the short friendships we have enjoyed together. It is part of the beautiful fabric of human life; the making a good connection with another. A few times I have had real assistance from these casual acquaintances and sometimes been able to help others.
Good travels are made better by being open to the people travelling around you.