101 Places to See was a book owned by Ellie Ravenwood, and later Clara Oswald, her daughter.
Clara kept it on a bookshelf with a number of other books on places such as America and India. It was her inspiration to go travelling after she finished university, but her plans changed and she became a nanny living with family friends. She kept the book as a reminder that she still intended to travel at some point, and in fact took it with her on her first (voluntary) trip in the TARDIS. (TV: The Rings of Akhaten)
In between the pages she kept an envelope, as well as a large leaf she referred to as "the first page". This leaf was instrumental in her parents meeting, and was kept because of its sentimental value.
On the first page she had also written "Property of Clara Oswald age 9". She then continued to replace her age each year, with the exception of 16 and 23, as she grew older until she was 24. (TV: The Bells of Saint John)