Well, this (humorous - I hope you find it as such) post are for those who spend about 10 ~ 15 min on the toilet. Might I suggest to read:
1. Note to Self: The Discipline of Preaching to Yourself by Joe Thorn
Quiet Time content. Each chapters are categorical and divided into days (~48 days) - various subjects such as relationships, spiritual discipline, love, etc. Short, concise, encouraging, easy to read, and engaging. 144 pages.
2. My Utmost for His Highest by Oswald Chambers
Quiet Time content. Popular book and many use this for their daily devotionals. Chapters are also categorical and divided into days (for the entire year). It might be a difficult read for some young readers but definitely one of my favorites. 416 pages.
3. 9Marks: Building Healthy Churches, series by various authors
You can find the series here. There are eight separate books in total and each specifically identifies "marks of a healthy church". I found this book extremely helpful in my growth. Books are short (around 150 pgs).
4. Is God anti-gay? by Sam Allberry
Informative short read on homosexuality. Perhaps not the best, but good enough for the toilet (not to demean this book in any way at all). The issue of God and homosexuality have been surfacing amongst our peers a lot lately and will continue to be a "hot topic." Whether you are for or against "homosexuality," my hope is that you find this read "informative." 88 pages.
5. Calvin & Hobbes by Bill Watterson
No Christianity jargon intended and because why not? And I like Calvin's dad; aspiring to be like him.
Hope you found this helpful. Enjoy the toilet while reading.