Counselors in my district get a small budget each year (same as teachers) to spend on instructional materials. Like others, I spend about all of it on books. My co-counselor and I's motto is generally "GET AAAALLLL OF THE BOOKS!". We use books in about 2/3 of our lessons and about 1/3-1/2 of individual and small group sessions. We love them. That said, we've found a lot of books to be flops (including some on other must have lists, so...it's a bit subjective).
If I moved to a new school and had to start from scratch, these are the books I'd try to get pronto. I tried to condense it but there are just too many great books out there. Shout out to my co-counselor who gave her input on ones for the younger grades which is far more her expertise than mine. Reminder: our population is Title 1 with a significant EL portion, so that shapes our views some!
Part 1: The Trudy Ludwig Collection
While you could definitely have a discussion about apologies (and how actions speak louder than words), I love to use this story to have a discussion on peer pressure and staying true to yourself. It opens the door for a discussion on choosing good friends and the value of popularity. Here's where I wrote up a lesson plan for this book and here are discussion cards to use for some quiz, quiz trade.