Going from bottom to top:
5. Red Rising by Pierce Brown. Best book ever, granted all of the books on this list could fit into that category.
4. The Iron Trial by Holly Black and Cassandra Clare. This book makes the list purely because it is signed by both authors and they are both on my favorite author list. Plus it is a good book.
3. Winger by Andrew Smith. As you are aware, this is my favorite contemporary book. I cannot wait for Stand-Off and we can all be extremely thankful that there was not a cover change. Andrew Smith is another one of those auto-buy authors for me!
2. Crown of Midnight by Sarah J. Maas. She is perfect and an amazing author. Crown of Midnight is my favorite of the series so far, even if Heir of Fire is more exciting in terms of character development. So I would pick this one to save granted I would want to save the whole series.
Let me know what your must save books are in the comments!