They can also do some handicrafts. For example, making jewelry out of beads or knitting a scarf. It not only kills time but also allows them to be creative and have something unique in the end.
For something modern, 'The Girl in the Wall' is a good choice. It has unexpected twists and turns that'll keep you on the edge of your seat. The build-up of tension is amazing when you're bored.
Fantasy fanfiction is a good option. These often have magical elements and unique creatures that can capture your imagination and keep you engrossed when you're feeling bored.
I'd recommend mystery novels like 'And Then There Were None'. The suspense will keep you on the edge of your seat and make you forget you were ever bored. Also, biographies like 'Steve Jobs' can be fascinating and inspiring.
The best book to read when bored actually varied from person to person. Different people have different preferences for different types of books. Some people like to read suspense novels, some people like to read science fiction novels, some people like to read martial arts novels. If you want to find a book that suits you, you can first understand your interests and preferences, then choose a novel that interests you and see if there are any works that suit you. You can also try to go to the library or bookstore to see if there are any books you like.