My desert island choices. I don't think they MUST be read, simply that they are the books I would cheerfully face shipwreck with.
Something by Barbara Pym. Today I'll go for Less than Angels, but I'd take pretty much any of hers. Funny and plangent.
The Debt to Pleasure, by John Lanchester for sheer good fun.
Non-fiction:
The Young Romantics, Daisy Hay. Haven't stopped thinking about this since I read it last year, particularly Claire Clairmont and how Byron took her little girl away.
The Lost Ark of the Covenant, by Tudor Parfitt. Invariably compared to Indiana Jones. Rattling good fund, a real-life quest through fascinating locations, not entirely without academic merit.
In Ruins, Christopher Woodward. If I say it's a kind of meditation on art history it makes it sound incredibly precious, but it's really accessible and eye-opening.