Have you ever wondered which book you would take to your Desert Island under the rule of 'one only' (and the Bible already there)?
How would you apply it to your holiday spot? Are you going to fly? If so, how heavy is the book? I know one person who took the Lloyd-Jones biography to Africa - but then he was using the long flight to read it for review.
Another practical problem is light to read by. Many holiday cottages are furnished on the principle that you will be out with the children all day on the beach, and in the evening you will be too exhausted to read, and so there is economy in the form of 40-watt bulbs. I have friends who take a 100-watt bulb of their own, just as I knew a boy who took his own bulb on blacked-out trains in the war, to give him enough light to do his homework on the journey back from school.