A - Well, sometimes it depends on what in particular the person is looking for or needs. But, if I were to give a short (yes, it really is a short list) then it would be something like this.
NOTE: This list generally has popular books that are easy for most people to read. In other words, while you will get good theology, it should not be too hard for a college-aged young adult to understand any of these books.
Source books & Must-have Magisterial documents
The Holy Bible – If you don’t have one and use it daily then the other books will be of little value.
The Catechism of the Catholic Church - If you don’t have it then get it and use it.
The Catechism of the Catholic Church - If you don’t have it then get it and use it.
Conversion stories:
Seven Story Mountain by Thomas Merton.
Surprised By Truth edited by Patrick Madrid.
Rome Sweet Home: Our Journey to Catholicism by Scott & Kimberly Hahn.
Born Fundamentalist, Born Again Catholic by Dave Currie
Evangelical Is Not Enough: Worship of God in Liturgy and Sacrament by Thomas Howard.
Set Free to Love: Lives Changed by the Theology of the Body by Marcel LeJeune.
Seven Story Mountain by Thomas Merton.
Surprised By Truth edited by Patrick Madrid.
Rome Sweet Home: Our Journey to Catholicism by Scott & Kimberly Hahn.
Born Fundamentalist, Born Again Catholic by Dave Currie
Evangelical Is Not Enough: Worship of God in Liturgy and Sacrament by Thomas Howard.
Set Free to Love: Lives Changed by the Theology of the Body by Marcel LeJeune.
General Q&A books or ones that have a very broad scope:
Catholicism by Fr. Robert Barron.
Handbook of Christian Apologetics by Peter Kreeft and Ronald Tacelli.
Handbook of Catholic Apologetics by Peter Kreeft and Ronald Tacelli.
A Biblical Defense of Catholicism by Dave Armstrong.
Catholic Christianity by Peter Kreeft
Church History:
The Faith of the Early Fathers. Edited by W. A. Jurgens, 3 volumes,
Where We Got the Bible: Our Debt to the Catholic Church. By Henry Graham.
Triumph by H. W. Crocker III.
What Went Wrong With Vatican II by Ralph McInerny
How the Reformation Happened by Hilaire Belloc
Characters of the Reformation by Hilaire Belloc
How the Catholic Church Built Western Civilization by Thomas Woods
Moral Issues:
Humanae Vitae Pope Paul VI
Good News About Sex and Marriage by Christopher West
Three Approaches to Abortion by Peter Kreeft
Theology of the Body for Beginners by Christopher West
Living The Good Life by Mark Lowery
An Introduction to Moral Theology William May
Catholicism by Fr. Robert Barron.
Handbook of Christian Apologetics by Peter Kreeft and Ronald Tacelli.
Handbook of Catholic Apologetics by Peter Kreeft and Ronald Tacelli.
A Biblical Defense of Catholicism by Dave Armstrong.
Catholic Christianity by Peter Kreeft
Church History:
The Faith of the Early Fathers. Edited by W. A. Jurgens, 3 volumes,
Where We Got the Bible: Our Debt to the Catholic Church. By Henry Graham.
Triumph by H. W. Crocker III.
What Went Wrong With Vatican II by Ralph McInerny
How the Reformation Happened by Hilaire Belloc
Characters of the Reformation by Hilaire Belloc
How the Catholic Church Built Western Civilization by Thomas Woods
Moral Issues:
Humanae Vitae Pope Paul VI
Good News About Sex and Marriage by Christopher West
Three Approaches to Abortion by Peter Kreeft
Theology of the Body for Beginners by Christopher West
Living The Good Life by Mark Lowery
An Introduction to Moral Theology William May
The Imitation of Christ by Thomas a Kempis
The Lord by Romano Guardini
Holiness – A Guide For Beginners by Dom Hubert Von Zeller
Listening at Prayer by Benedict Groeschel
Introduction to the Devout Life by Francis de Sales
The Practice of the Presence of God by Brother Lawrence
Spiritual Direction and Meditation by Thomas Merton
Prayer: The Great Conversation by Peter Kreeft
I Believe in Love by Jean C.J. d'Elbee
The Fire Within by Thomas Dubay
Other works not necessarily in only one category or in no category:
Theology and Sanity By Frank Sheed
Theology for Beginners By Frank Sheed
Mere Christianity by C. S. Lewis
The Screwtape Letters by C.S. Lewis – Another masterpiece
The Great Divorce by C.S. Lewis – Heaven is in our grasp.
The Godless Delusion: A Catholic Challenge to Modern Atheism by Patrick Madrid and Kenneth Hensley
The Journey: A Spiritual Roadmap for Modern Pilgrims Kreeft, Peter
How to Win the Culture War by Peter Kreeft
The Lamb’s Supper by Scott Hahn
Making Senses Out Of Scripture Mark Shea
Where Is That In the Bible? by Patrick Madrid
A Refutation of Moral Relativism by Peter Kreeft
How Not to Share Your Faith by Mark Brumley
Hail, Holy Queen by Scott Hahn
The Rhythm of Life by Matthew Kelly
The How-To Book of the Mass by Michael Dubruiel
Letters to a Young Catholic by George Weigel
Catholicism and Fundamentalism. Karl Keating
By What Authority? Mark Shea
Render Unto Caesar by Archbishop Charles Chaput
The Church and New Media Edited by Brandon Vogt
The Loser Letters by Mary Eberstadt
I hope this helps. You can check out all of these in St. Mary's library.