are characteristics, behaviors, or objects (things) which can be associated with the English and English society. These might be warm beer, full English breakfast, chicken tikka masala, tea, St. George's Cross, bulldogs, the English language, and of course, The Queen.
Jane Hawking is saying that "joining a church choir" is a stereotypical English thing to do. Jane Hawking was a Catholic and female, and church choir is considered a safe place to spend time.
The same could be said if Jane was told to "Have a cuppa tea, and think it over."
Other examples are
might be kimonos, sushi, kabuki, geisha, and overcrowded subways.
might be kilts, bagpipes, whiskey, haggis, and deep-fried mars bars.