How is the book The Fault in Our Stars different from the movie?

The differences between the Fault in Our Stars movie and book are very minimal considering the vast differences that usually occur in a book-to-movie adaptation. While the key points and development of the story remain unchanged in the movie, there are a few smaller details that were altered, either for stylistic reasons or simply because the movie version could not encompass as much detail as the novel.
For instance, when Gus and Hazel are in Amsterdam, their romantic dinner takes place outside in the novel, but in the movie they have their dinner inside instead. Also, during this romantic dinner in the movie, Gus proclaims his love for Hazel, but in the novel, he proclaims his love on the plane ride to Amsterdam. The reasons behind these decisions could potentially be explained by the film's director, Josh Boone, as I am sure he had a creative vision that he wanted to carry out within the movie.
A few other minor differences are that Hazel has a friend named Kaitlyn in the book, but Kaitlyn does not appear in the movie. Also, Hazel goes to visit Isaac in the hospital following his surgery in the novel, but this interaction is not shown in the movie. Gus's older sisters and their husbands and children play a key role in the novel, but they are scarcely mentioned in the movie.
Another difference between the two is that Hazel sells her beloved, though neglected, swing set in the novel, but she does not part ways with it in the movie.
These details, though present and powerful within the novel, are not included in the movie. This could be purely based off the director's vision or lack of time to carry out the story properly while still including each small detail from the novel. Either way, the movie version is very similar to the book itself in that it contains all the essential plot points and many of the beloved quotes from the novel.